THEY do say that if you talk to yourself, you can at least be sure of a sensible conversation. This just doesn't ring true, because as far as I can judge, talking to oneself seems to be an early indicator of madness.

I'm not saying the young postman I saw the other day was on the road to the mental hospital (he was actually between the church and the crossroads by the pub) but he certainly appeared to be a few junk letters short of a sackful.

I was waiting at a red traffic light, with the car window open, and heard the sound of an approaching voice. These days, a lone person walking along the street and indulging in an animated conversation is most likely to be talking on a mobile phone. Sometimes, they do it via a little earpiece and a microphone so there is not even the familiar hand-to-the-ear posture to give the game away.

But this chap was in ongoing dialogue with himself, apparently quite oblivious to the outside world, and judging from the snatches of conversation I heard, he was not a happy chap. Not just because he was scattering rubber bands on the footpath - that seems to be a habit with postmen, who presumably have industrial-sized boxes of them back at the sorting office and don't have to bring back the used ones at the end of their round. Like people who use a foot of Sellotape around a parcel when a couple of inches at each end would do the job, this throw-away attitude offends the waste-not-want-not philosophy that was drummed into me as a kid.

But the general turmoil and anger evident in the young postman's monologue seemed pretty typical of this phenomenon.

It's a sad thought, but he may go on to become one of those elderly, dishevelled men of no fixed abode who shout at traffic. Agreed, traffic is a nuisance, not least when you're a pedestrian and you can't cross the road, but to stand on a street corner hurling a torrent of abuse and obscenities at vehicles in general is a little bizarre, to say the least, and the best course of action - albeit a little lacking in compassion - is probably to give them a wide berth.

This, however, was not possible with a young man called Robert, with whom I once shared an office. He was a messenger and he had the wildest eyes I have ever seen in a person. They screamed "Axe Murderer". Robert had the curious habit of saying very little in the office, particularly when asked a question like "Did you post those letters?" or "Any chance of popping out to get a couple of bacon sandwiches?" He saved all his words for the men's lavatories, where he locked himself in a cubicle and carried on furious solo conversations, at the top of his voice.

It was quite unnerving to walk into the toilet and hear all this going on behind a closed door and I was not the only man in the office - when chancing upon Robert in full voice - to decide that perhaps the need to relieve myself wasn't so pressing after all... or find another lavatory in the building.

Just one thing worries me, though. As an only child, I depended on the company of friends, rather than a brother or a sister. But my mother, bless her, didn't like the kids I played with in my early primary school days. She called them "those rough boys from the council estate" and wouldn't have them in the garden.

Not allowed out, to see what naughtiness the rough boys were up to, I was obliged to play alone in the garden and invented all sorts of games to pass the time. And it was then that I developed the habit of thinking in the first person plural. "I" became "we", which is sad. All these years later, I can only hope that if I was going to turn into the sort who talks to himself and shouts at traffic, I'd have been doing it by now. Wouldn't we?