Harriet Walker: There are only four types of jeans-wearer

To most people, fashion is not this season's candy colours. To most people, fashion is not even next season's shiny vinyl and leather separates. To most people, fashion is just a pair of jeans and a nice jumper.

This much I have realised as I have grown older and things have started creaking, now that I can't be bothered to cram myself into an outfit worthy of a Ziegfeld Follies girl every day. I have realised that heels before 8pm are a hassle and after 8pm are a hindrance, that tight things aren't right, and that effort is overrated.

The people you see at Fashion Week, the ones who really quicken your pulse and make your heart twang in dispirited envy because they look so good, are not the ones in the ballgown and matching hat. More often than not, they're in jeans and a jumper. And trainers! How I long to be the sort of person who looks good in a pair of trainers!

It strikes me that everyone has a mode of dressing that is singular to them – an entirely social construct, of course, according to habit. But dressing beyond your ken feels as wrong as brushing your teeth with your left hand.

I have a quadrant of friends who are incredibly posh and like to wear rugby shorts – even the girls, who wear normal clothes by day and then slob around in a London Wasps number in the evening or on Sundays. The last time I stayed the night, my friend offered me something similar to sleep in, then collapsed into giggles when I put it on. "It just looks so… wrong. On you, I mean. You look like a middle-aged man with long hair." This delivered while wiping tears of hilarity away with one hand and playing with her perfect posh person's hair with the other.

I told myself it was because I am normally so elegant that sportswear just doesn't sit with my sartorial DNA. But I think I knew at heart that it was because only posh girls look good in rugby kit.

I used to have the same problem with jeans. I realise this is odd, given that jeans are basically the only thing that anyone wears, and that all those ditsy floral-print playsuits in the shops will hang there until the apocalypse happens because we'll all be knocking round in our 501s until our dying breath.

Yet, for all that we live in our jeans, for all that denim was possibly one of the best inventions ever, they remain a right bugger, don't they? Because they're a nightmare to get right and no matter how hard you try, you always fall into one of the four elemental jeans categories…

1. The Dad Jean: a sturdy straight leg made from pristine blue denim that is neither faded nor distressed. A blue so blue you might be fooled into thinking these were chinos. But wait, what's that? A phone holder, coin purse and utility belt attached to the waistband? This is the heady pragmatism of the Dad Jean.

2. The Ageing Rocker Jean: when I worked in a pub as a student, one of the regulars used to team his slim-fitting, ripped stonewash strides with a Levellers jumper (guffaw). It took me years to realise that it doesn't matter what the band on your top, wear it with jeans and you're officially in Ageing Rocker territory.

3. The WAG Jean: a low-rise style that starts around the pudenda and falls to a kick flare, obscuring your feet so you move as if hovering, like a baddie pretending to be a ghost in Scooby Doo. This style has a distinct relative in the more obscure high-waisted flared jean that someone tries to revive every five years, before realising they make everyone look like they're in the Brotherhood of Man.

4. The Skinny Jean: the social affliction de nos jours. Regardless of how awful they look, you have to wear them because they're the only style deemed fashionable and acceptable. Sorry.

Recently, I managed to find a pair long enough to wrinkle up a bit at the ankle (I won't have anything flapping about down there at half-mast) with plenty of stretch and – this is the exciting bit – a high waistband that not only means not an inch of my posterior is on show, but also offers the happy situation whereby you can stuff all the excess flesh on your torso into the waistband, as if you're proving bread dough.

I used to think I looked odd in jeans – perhaps I still do and I just care less. But I think my recent change of heart is not related to this, so much as a breakdown in the part of my brain that regulates how long you can stay in bed versus how long you spend choosing an outfit. And so I find myself wearing my jeans nearly all the time – when I'm not in bed, that is. That's just how fashionable I am.