This charming man: Who is the real John Mayer?

He's a regular in the gossip magazines, an obsessive Twitterer and an unapologetic alpha male. Oh, and he's also sold 13 million records.

John Mayer isn't convinced he should be doing this interview. Not here. Not now. Not like this. He's just throwing ideas out there, but why, he asks his publicist, "couldn't we do all interviews via a hub, fibre- optically? Why aren't artists sitting in a Sony boardroom somewhere with a Cisco video conferencing system, talking to journalists in London, Jakarta, Australia?" Human contact is a good thing, she replies; it helps readers to feel a little closer to John Mayer.

After all, if we weren't sitting in this plush hotel room, with the expensive German chocolates, the throw-cushion collection and the view of Hyde Park, I couldn't honestly describe Mayer's heavy-lidded brown eyes; his absent-minded twirling of that not- inconsiderable quiff; or the moment when, perching on the edge of the sofa, dangling one Converse-covered foot in the air like a chimpanzee, he starts miming vigorous masturbation and – is he really? Yeah, he definitely is – self-fellation: "There are certain things your microphone can't pick up," he says excitedly. "Ain't it great?" Would I really get the same experience from a glorified conference call?

Being a John Mayer fan is rewarding, but it can be hard work, too. Even though he sold out the Hammersmith Apollo in three hours, getting fellow Brits to put a face to his name is nigh-on impossible until you mention the celebrity ex-girlfriends: Jennifer Love Hewitt, Jessica Simpson, Jennifer Aniston, Jennifer Aniston again. "Ooooh," they go. "The love-rat guy." The albums Mayer recorded before even meeting Aniston sold 13m copies and won him seven Grammy awards but, inevitably, those same Brits equate his recording career with the magazines they have seen him in: not Q or The Word, but Heat and Grazia.

Which is unfortunate, because watching Mayer play a virtuoso guitar solo is a lot more exciting than flicking through photographs of his love-life. He's a consummate musician and frequently an inspired songwriter. His deceptively complex compositions contain volumes of American music history, from Marvin Gaye's soul to Buddy Guy's blues. Just ask the roof-raising crowd at the Apollo, where his set list contains covers of Robert Johnson's "Crossroads" and Tom Petty's "Free Fallin'", alongside his own impressive back catalogue.

Problem is, just as you've finally convinced the sceptics of these substantial musical chops, Mayer makes a risqué joke that goes down badly with the Grazia demographic, and you have to start defending him all over again. Ten days prior to our interview, before a small crowd of competition winners and industry types at London's Hard Rock Café, Mayer banters between acoustic numbers about abortion, drugs, Christian rock and getting an audience member pregnant. In the context, it's all pretty funny. Really. But a day or two later, when it makes it into the red-tops, the jokes are described as "shocking", and the chuckling crowd as "stunned".

"What? You can't say the word 'abortion'?" he asks, incredulous. "Were you offended?" Er ... no. "Was the person standing next to you offended?" I don't believe so. "Was anyone you know offended?" Well, I'm not sure my granny would've been into it, but I get his point. "It's just people's assumption of what's going too far. I'm a rock guy, not a kindergarten teacher. We can be lewd. There are things that I could do that could be going too far that could literally make the audience turn their tickets in. But standing on stage with a twinkle in your eye and saying 'somebody's getting pregnant tonight' is cute. I'm just goofing off. When journalists ask 'Did he go too far?', they make rock fans sound like pansies."

Goofing off is standard practice in Mayerland. He has been known to take the stage at New York comedy clubs – and, indeed, tell a few decent jokes while he's up there. He has mastered the art of the witty, semi-revealing tweet ("If you call a girl 62 times and she's sleeping, does it read in the morning as one missed call or 62? Asking for a friend") and now has just shy of 3 million Twitter followers. This Chrismukkah he held an "Interfaith Holiday Baking Contest", offering prizes (including a kitschy Christmas sweater he'd worn on Ellen) to the fan who baked the most impressive seasonally themed cake. He makes a habit of wearing outrageous fancy dress on his exclusive annual "Mayercraft Carrier" cruise; in 2008 he donned a Borat "mankini" to jog around the deck. One ambition when he was starting out, he says, was not only to play his music on The Tonight Show, but also to crack up its presenter Jay Leno from the couch. He's gone one better than that: his own prime-time network variety show, John Mayer Has a TV Show, is in the works.

Mayer's media résumé also includes a spell as a columnist for Esquire, and he chronicled the recording of his latest CD, Battle Studies, with a series of YouTube videos and blogs (an insightful post defending Avatar director James Cameron from a smear by one celebrity gossip website TMZ.com, earned him a job offer from another, Gawker.com). Social media is just one of his many avowed obsessions, alongside the guitar, first-person shooter video games, Japan, pornography, design – he oversees all of his own album artwork – and the Israeli martial art, Krav Maga. He collects trainers, handbags, old Land Rover Defenders, cameras. His watch collection is worth over $20m.

"I've always just been stupidly curious about stuff; I'm not diversifying in terms of selling anything," he explains. "I'm not selling 'John Mayer: the cologne'. If I did it would just smell like sausage and sleep. I don't look at my fans and think, 'Wow, they really like what I do musically. Imagine if I could get 60 more dollars out of them.' Who out there really goes, 'You know what, I just fucking love perfumes. I always have since I was a kid. If I weren't a pop singer, I'd be a perfumier ... '? At some point I may turn into an asshole, but right now I just peddle a CD for 15 dollars every two years."

Born in Connecticut in October 1977, Mayer first picked up a guitar after watching Michael J Fox play one in Back to the Future. When he was given a Stevie Ray Vaughan cassette by a neighbour as a young teen, his fascination with the instrument grew into a passion; the initials "SRV" now form part of the full-sleeve tattoo on his left arm. His parents, both schoolteachers, had watched many of their students neglect their education in the vain pursuit of sports stardom. They didn't want the same to happen to their son, and for a long time resisted his musical ambitions.

But a driven Mayer wouldn't be deterred. "My daddy didn't reach into his wallet and hand me talent or songwriting skills," he says. "I did that myself. I worked for it, and I still work for it." After high school, he won a place at Boston's Berklee College of Music, but after two semesters dropped out and headed south – to Atlanta, where the singer-songwriter scene was in rude health. After getting the attention of the A&R men at the South by Southwest festival in Austin, Texas in 2000, he was signed to Columbia Records.

His first two albums, Room For Squares (2001) and Heavier Things (2003), were accomplished singer-songwriter fare. Their two hit singles, "Your Body is a Wonderland" and "Daughters", made Mayer a pop star – but he was not-so-secretly a rock guy even then: "Wonderland" might sound like a sweet acoustic love song, but it's really an ode to foreplay. In 2005, he teamed up with two old rock hands, drummer Steve Jordan (who'd played with Keith Richards and Bruce Springsteen) and bassist Pino Palladino (who joined The Who following John Entwistle's death) to form the John Mayer Trio. Together they recorded the blues-rock live album Try!, and soon Mayer was being mentioned in the same breath as his friend Eric Clapton. Jordan is still a musical soulmate – he co-produced Battle Studies and is just one of a clutch of formidably experienced musicians in Mayer's touring band.

"I'm trying to write tunes in a classic form," says Mayer, who has cited Petty and Neil Young among his recent influences. "I'm not saying they're classic songs, just that they're in classic American song form. So it's obvious to go to people who've played on dozens of those records. If you're directing a movie about boxing, you want to get some big motherfuckers in your movie. I want to play with the best guys around."

Thanks to the unfashionability of the genre, he hasn't much competition, but Mayer is arguably the great classic rock guitarist of his generation. In 2006, he released his third and – in most people's opinion, including his – best studio album, Continuum. Yet just as his artistic credentials became unassailable, he started dating Jessica Simpson, and suddenly he was a tabloid fixture, too, acting up for the paparazzi and setting off flame wars with Perez Hilton.

There have been other celebrity flings since Simpson, but nothing could match the attention he received for his on-off relationship with Jennifer Aniston, which ended in March last year. I've been instructed not to discuss it in our interview, but Mayer has already said the break-up was one of the worst times of his life – and besides, he's written an entire album about it. Just look at some of the titles on Battle Studies: "Heartbreak Warfare", "All We Ever Do Is Say Goodbye", "Perfectly Lonely", "Friends, Lovers or Nothing". After the couple originally split, Mayer delivered a mea culpa to a TMZ video camera on the street outside his New York gym ("I'm the asshole. I burned the American flag. I basically murdered an ideal"), a noble but probably inadvisable act. Fiercely self-aware, Mayer's over-thinking translates into over- sharing, and his relationship with the celebrity press frequently involves him saying what seems like too much.

"It's a compulsion," he admits. "I would tell you that I wish I didn't say these things because I don't like the way it feels after I've said it, but I'm just gonna say more shit just like it. If you already know who you are, you should probably just have a beer with yourself and go: 'We're cool, it's gonna happen again and again'."

Then again, I suspect it's also his way of undermining the media, of taking ownership of the tittle-tattle around his private life before anyone else can. "Absolutely. I didn't know that until I'd been doing it for a while and asking myself why I kept doing it. It's just defensive manoeuvring."

Nowadays, Mayer is single – and keen to emphasise the fact. I try to contrast his famously loose lips with the furious control that Tiger Woods exerted over his image, and which contributed to his public downfall. But he's having none of it. In fact, it sets him off on one of his energetic soliloquys – referring to himself in the third person, doing funny voices and so forth. "No. Tiger Woods' problems come from him being married. The end. It has nothing to do with control. If Tiger Woods was a single guy, what sort of angle would there be to a text message? If Tiger Woods was single, and he texted a girl and said 'I wanna wear your ass like a hat', why would that ever hit the news?

"I can text whatever I want to anybody in the world; I'm not married. I write a lot of dirty text messages to girls, and you've never seen any of them. Why? Because if a girl brought a dirty text message from me to the newspapers, they'd say 'I don't have an angle here. Someone wants to wear your ass like a hat? Big deal. He's 32 years old. He's a single guy. If John Mayer has a wife and sends dirty texts, then we got a story.' And that's why I won't do that. When I get married that's gonna be my vows, 'Do you, John Mayer, take this woman to have and to hold, to wear her ass like headgear?' Yes, I do – you're the one whose ass I wanna wear like a hat for the rest of my life." And then somewhere in there is the reflective, slightly wounded Mayer, who evidently takes at least a little of his tabloid-bashing to heart. "With this whole Tiger Woods situation," he says, "I wish more people would be like, 'You know what, Mayer? You didn't fuck up at all.'"

A straw poll of my friends – the few that knew a thing or two about him already –produces two distinct theories of Mayer. First, that he's a nerd, a geek, who has transformed himself into an alpha male through music and sheer willpower: "It's possible to not have it all when you're a kid," he suggests, "and be smart enough to say, 'This is what I want to add to myself.'" Second, that he's a jock pretending to have a sensitive side. "Well, I wanna beat the shit out of whoever said that," he replies instantly, that 'gone-too-far?' twinkle in his eye again. The truth is a little bit of both. Sure, he's a nerd – but everybody's a nerd now. "The girl you wanna sleep with the most in the bar, the dumb blonde with the big boobs? She's got a Facebook page. She's got a Twitter. She can set her TCP/IP preferences. 'Nerd' is an antiquated term."

And he definitely is a jock, with a recently acquired physique to match. When he asked a friend why bloggers had begun to call him a "douchebag" – a word so resonant that he wrote a lengthy blog post about its qualities and meaning himself – "She said, 'Well, all of a sudden you go work out, you get in shape and you're buff all the time ... ' And I was like, 'What is wrong with that? Because I eat an egg-white omelette in the morning I think I'm better than you?'"

Mayer can't abide this attitude, which is why his best friends are fellow alpha males. "I don't have another musician in my close group of friends. There's a guy who produces movies and he's incredible at what he does. Bob Maron, one of my best friends, is one of the best watch dealers in the world. My friend Tony Held makes the best iPod cases.

"I like being around people who don't bite their nails and go, 'It'll never be me.' It will be you if you work hard enough at it, you putz. It's a real male thing. It's like, 'Here comes Mayer, he's probably gonna one-up me.' Like they think I'm gonna throw their girlfriend on the bar and fuck her in front of them. No, I actually have respect for other people. I understand some people get offended because I don't always vocalise my doubts, but I've never met anyone who, at the end of the day, after hanging out, went, 'Hey Mayer, I gotta say, you're still a douchebag.' No one ever did that. They're like, 'You're a pretty cool guy.'"

Don't for a minute think it's difficult being John Mayer, or that he's trying to give you that impression. The video for his recent single "Who Says" was filmed on location at his Manhattan apartment and a few favourite New York haunts. It starred the aforementioned alpha friends and a gaggle of beautiful women eating, drinking, and dancing the night away. ("The friends are real," he confirms. "The girls were hired.") It looks an enviable existence; one great, never-ending Entourage episode . After reading another recent interview with himself, Mayer tweeted: "I'm still not sure if I would want to hang out with me." I suspect he has a long list of worries, but finding people who want to hang out with him needn't be one of them.

Tickets for John Mayer's UK arena tour go on sale tomorrow. Battle Studies is out now.Mayer Studies: Tim Walker's introduction to John MayerTry!ContinuumBattle StudiesHeavier ThingsTry!Battle StudiesContinuumNo Such ThingDaughtersBattle StudiesWhere The Light Is: John Mayer Live In Los AngelesContinuumClick here to listen to the playlist on Spotify(free registration required)