As anyone who knows me will attest, I'm a pretty mild-mannered person. (I can hear those who know me very well respond wearily: really?) Anyway, I found myself yesterday in the unusual position of feeling a visceral hate towards someone merely on sight.

I was on a bus in the rush hour, and this man got on while talking very loudly on his mobile phone. "Absolutely," he kept repeating. Everyone else swiped their Oyster cards, but he just stood there barking into his mobile while casually searching his pockets for his own card. The packed bus couldn't move until he found his card, but he seemed unaware of this, continuing his conversation for everyone to hear.

"There's plenty more where that came from," he said at one point, leaving a bus-full of strangers to hope that, in fact, there wasn't. Eventually, he succeeded in locating his card and the bus was able to move off. Undeterred by the force field of antipathy around him, he didn't miss a beat. "Absolutely," he continued, "I get it completely."

I found myself convulsed with loathing, and not just because of what I considered anti-social behaviour. Was it his clothes? He was wearing yellow corduroy trousers, a red V-necked jumper and a Barbour-style checked coat, and I've always thought it is an indictable offence to wear country garb in a built-up area. Or was it his high-handedness, making the bus driver (and the other passengers) wait until he was ready? There was something about his self-satisfied tone, too.

And then I realised. I hated myself. I hated the fact that I hadn't tapped him on the shoulder and said: "Excuse me, do you mind not talking so loud. Not everyone wants to hear your telephone conversation." That's all it would have taken. A simple, polite request and I am sure he would have desisted.

The truth is, sadly, that I'm not that sort of person. I'm not the one who makes a fuss. In fact, I'm the one who gets slightly embarrassed when someone else does. I have always wished I was more like Larry David in Curb Your Enthusiasm, who is always pulling strangers up for what he perceives to be anti-social acts, such as cutting in on a queue on the pretence of meeting someone (the old cut-and-chat manoeuvre).

Of course, there's something noble and heroic about such behaviour, and I'm sure that had I remonstrated with the man on the bus I would have been admired by my fellow passengers. But I would have no sooner done that than driven the bus away.

It is one of the problems of public transport: at some stage, you are going to be confronted with a situation where you have to act counter-naturally, whether it be having the moral rectitude to pick an argument with a stranger or showing physical courage in a potentially dangerous situation. It is one of the modern world's small challenges.

Follow @Simon_Kelner