Some time ago I had lunch with the chief executive of a well-known company in the City of London. He told me that every time he goes to a dinner party, he turns to the guests either side of him and offers unsolicited feedback on the quality of their conversation during the meal. So, he might tell someone that while he'd enjoyed listening to their views on the Chilcot inquiry, they could have made more eye contact and asked him a few questions. Or that, although he was interested to hear about the choice of schools for their children, they could have kept it briefer or been a little less boastful.

When he told me this I was shocked. How vulgar, I thought. Yet every time I've been out to dinner and sat next to people who were not pulling their weight, I have thought about him and wished that I was brave enough to offer tips on how they could improve.

Last Monday night, I sat next to a senior banker at a large formal function. He was intelligent and had a nice smile, and I thought we were getting along rather well. When coffee had been dispatched, his wife came up to him and asked if he was ready to leave.

“I'm desperate to go,” he declared loudly.

Because I'd had rather more alcohol than was wise on a Monday night, I found myself telling him this was incredibly rude. That until that point I had enjoyed his company, but now the effect was spoilt.

This, I decided, was perfect feedback. It was spontaneous and heartfelt and specific, delivered in real time, eyeball to eyeball. Judging by the expression on his face, I'm pretty sure it hit home.

Earlier on that evening, I had given some rather less perfect feedback. I'd been getting ready to go out when a man appeared on the doorstep with a clipboard trying to raise money for a homeless charity. He was a bit pathetic and so I asked him in. Agonisingly slowly, he filled in the standing order forms and, when he was done, he fished out another set of much longer ones. Would I mind giving some feedback? So I ploughed through two pages of questions. How well informed did you feel about the charity? How polite was he? I ticked a few boxes more or less at random and sent him on his way.

This exercise destroyed any virtuous glow I might have felt and was utterly useless. The only relevant information about a fundraiser is whether he raises funds; and this particular man had just hit a – rather meagre – jackpot.

Feedback is a bad word, and it's a bad business. There is no longer any transaction or any business relationship that does not require feedback. I am endlessly invited to fill in forms to describe my feelings towards my employers, my children's headmaster, the board of the company where I am a non-executive director and towards the man who has just unblocked the drain.

Feedback forms are hopeless, because the wrong questions are asked at the wrong time to people who generally are in no frame of mind to answer them properly. And then they are filed away, the main action being that pie charts are drawn to depict the results.

Feedback matters because it is useful to discover what other people think. Unfortunately, there is no formulaic way of finding this out. The only way is to do it spontaneously.

The best people at giving spontaneous feedback are one's teenage children. Not all of their feedback is of obvious practical use: “You're a bitch” does not help you stop being one. But teenagers are invaluable when it comes to telling you your voice sounds insincere or that a new dress you've bought looks hideous. Whereas nothing has ever changed as a result of any box I've ticked on a form, thanks to teenage feedback I have given the dress away and try to sound more genuine.

The problem with adopting the teenage model of feedback at work is fear. We don't speak out because we are afraid, and often with reason. But a company in which people are afraid to speak their minds is not going to be helped by any feedback forms sent out by HR either.

The problem with adopting it at dinner parties is manners. Yet this is misguided. If you accept an invitation to dinner you are entering into a contract that says: I am being fed and in return I am going to try hard to be interesting and interested. To the extent to which people do not honour their contracts, they should be firmly told. To give such feedback is not rude or vulgar. It's a public service.