Rage: an everyday story of fear and intimidation in the capital

London is angry, writes novelist and native New Yorker Douglas Kennedy, and it's getting angrier

She was around 30 – blonde, aerobically primed, well-dressed in a short, expensive leather jacket and designer jeans; the sort of metropolitan woman who carefully considered her public appearance before leaving the house. She was standing behind us at the checkout of the Marks & Spencer foodhall in Marble Arch. By us, I mean my wife Grace and our two children, Max and Amelia. We had just finished that usual bit of weekend banality, better known as the big shop, and were about to move off towards the exit, when suddenly there was a voice behind us, a voice that took us aback with its violence and unexpectedness. (No doubt it will shock you, too. I do not repeat these words, or the rest of this sorry, sordid tale, lightly.) "Move your fucking trolley."

Grace turned around, looking just a little thrown by this angry comment, which was being hurled directly at her. It was that woman. She spoke in a definitive estuary accent, and was pointing to the shopping trolley that, in our rush to get all the shopping packed, we had accidentally left behind in the aisle. Grace looked at her squarely and said: "You don't have to be so rude," to which the woman replied: "Well, you fucking left it there." At which point I entered the conversation, telling Ms Politesse: "You are an exceptionally unpleasant woman."

Within a nanosecond of that comment, I was being confronted by her guy. He was around three inches shorter than me, built like a pit bull, with the sort of hands that looked like crude Soviet-era industrial machinery. He pushed his face into mine, and said: "Don't you fucking talk to my wife that way."

I said nothing. I just met his stare, trying to remain as calm as possible (no easy task), while all the time wondering if he was going to hit me. "You going to fucking say something or what?" he demanded. But I simply kept eyeballing him, willing him to flinch. (The gentler readers among you may wish to flinch no more and turn the page here). He did, by hissing at me: "American cunt." I said nothing. So he repeated his comment once more. But when I failed to respond again, he backed off. I picked up my bags and joined Grace, who had shrewdly shepherded our children out of the eye of this moronic storm. But as I walked away, the woman yelled: "Go back to America, cunt."

Now I have lived in London for nearly 15 years, and I genuinely like it here. In fact, I'd go as far to say that London has been very good to me. And as I was raised in another mega-metropolis, New York, I am well used to the indifferent, edgy stress-and-strain that is big-city life, not to mention its inherent scenic grubbiness. Cities are not tidy places, and historically London has never been known as a paragon of anal retentive spruceness.

But since that exceptionally ugly confrontation in Marks & Spencer, Grace and I have related this story to assorted friends, all of whom have come back with their own tales of trolley rage, road rage, Tube rage, pavement rage, pushbike rage, and other civic rudeness.

Consider my neighbour in south London. She is an exceedingly polite, cultured woman who, one Saturday morning a few weeks ago, went outside to speak to two workmen who were manufacturing tar for a house under renovation next to her own. Their noisy, smoke-billowing machine was driving her just a little spare, especially as she also happens to be seven months pregnant. But when she approached one of the workmen and gently asked how long the tar-making was going to last, he said: "I don't fucking know. I didn't want to work on a fucking Saturday, did I?"

This level of boorish discourse now seems commonplace in London, especially when compared to the two other big metropolitan sprawls with which I am in regular contact: New York and Paris. Indeed, both of these cities are noted for their brusqueness, their suffer-no-fools world view. But as a native Manhattanite, and as someone who now divides his time between London and the French capital, it is intriguing to note the different styles of rudeness as practised in the three cities. Whereas New Yorkers became born-again polite in the aftermath of 11 September, by the time I revisited the city a few months ago, the old gruffness had re-established itself. But New York discourtesy is based on a certain hyper-pressured "time is money" principle. Fools and tourists are put down for naivety, and hailing a cab during rush hour is something of a competitive game. But it rarely turns into the sort of rage that you can now often encounter in this country. Yes, New Yorkers are arrogant, and yes, you can still get mugged if you're in the wrong place at the wrong time, but you're mugged for money, not for aggressive sport.

Parisians, on the other hand, are often accused of impoliteness. This always strikes me as surprising, considering that French society demands such a high level of public politesse, to the point where all conversations in a shop must start with bonjour , and where using the tu form of address or colloquial argot among those not known to you is also looked upon as seriously not right (a twentysomething slacker working in a used record shop near the Sorbonne was genuinely taken aback when I used the word fric – slang for money – when talking to him about the price of a CD. "Have we met before?" was his surprised response, because I used un mot familier).

Granted, Parisians are undeniably haughty, but during the past two years that I have called that city my part-time home, I have yet to see the sort of verbally abusive public incident involving strangers that now seems such a sad facet of London life. And whenever I return to London after a stint in Paris, two things immediately strike me. The first is that without question, this is the most culturally dynamic city imaginable, and secondly it is also such a desperately angry place. Of course, one could engage in a rant about the decline and fall of good manners, and blame it on a lack of indoctrinated decorum, declining moral standards, the failure of 1960s liberalism, and other such neo-conservative rants. Similarly, one could jump to the other side of the ideological fence, and point out that, from Thatcherism onwards, we have witnessed a marked decline in the idea of community, coupled with the accelerated growth of the culture of self-interest. The shabby state of essential services – especially public transport – could also be blamed, as could the sheer density and vastness of London, especially when compared to the relative compactness of Manhattan or Paris. And then there's the great ongoing fact of English life: the way class defines so much of social interaction as anyone who's ever been verbally assailed by a white van man well knows.

But trying to pinpoint the socio-political reasons for general impoliteness is one of those thankless tasks best left to sociologists or the Prime Minister's strategy unit. What I will say is that London seems to have become the sort of urban pressure cooker in which people explode for the most prosaic of reasons, and where we seem to have lost the basic, necessary human skill of showing a modicum of respect to those who cross our path. We have become an irate metropolis, where the knee-jerk reaction is to scream "wanker" when somebody edges their car into our lane, and where we have begun to regard each other as potential antagonists. And that is sad. Impoliteness not only corrodes our view of others, it is also toxic. And like all toxic substances, it poisons the way we live.