Would you talk to a farmer about BSE? Of course not. Everybody has their sore point, explains Hester Lacey
There are those people, at parties, who mix effortlessly, glowing chatter flowing from their lips. And there are those who, like the "I'll get me coat" chap in The Fast Show, equally effortlessly create the conversational equivalent of a black hole. Brick-dropping in a roomful of strangers is frighteningly easy - particularly once the fateful question "What do you do?" has been tossed into the arena. It's pretty obvious that telling a farmer you haven't dared to touch beef since 1993 won't go down too well, but there are plenty of other no-go subjects to tiptoe around.

One mistake that is guaranteed to lead to the cold shoulder is to try to cadge a bit of free consultation. "It is amazing how many people just happen to be looking for a job when I meet them," says Chris Mackintosh, recruitment consultant. "Before I know where I am, they're reeling off their CVs - right down to the last O-level and swimming certificate - and asking what kind of salary they can get."

"You'd be surprised how many people will ask you for a quick on-the-spot diagnosis, once they find you're a doctor," says Ann Hale, an equally indignant medic. "They'll be going on about phlegm and expectorating or virtually dropping their trousers to show you their boils. I'm afraid I tend to be quite rude and suggest they make an appointment with their GP - either that or I say that I specialise in 'unmentionables', which usually shuts them up."

Humour should be applied with caution when it is at the expense of other people's jobs. Should you meet a journalist at a party this Christmas, do not be surprised if they fail to dissolve with laughter at any opening gambit along the lines of, "Ooh, I'd better watch what I say, in case you write it down! I expect you've got your tape recorder running!" Because everyone says that, and it's, erm, unlikely, to say the least. Equally, avoid squaring up to them about the death of Diana, Princess of Wales (particularly if they are, say, a cookery writer).

Similarly, policemen are not cracked up by jocular quips along the lines of "Better be on my best behaviour, then!" ("It makes me really, really want to arrest the sad bastards, believe me," says one who prefers not to give his name.)

"If one more person asks me if my job is really as dull as it's supposed to be, ho ho ho, I may hit them," snarls a normally mild-mannered accountant. It's an old truism that most people like to be gently encouraged to talk about themselves. But not to give an entire lecture/presentation to an audience of one. "Some woman the other day said to me: 'Now, I want you to explain all about the Internet to me - it sounds fascinating!' and then she cocked her head to one side, opened her eyes wide and waited, all smiles," wails Annick Petersen, a computer programmer.

"I hate it when people say: 'Oh, a teacher! And where does your school come in the league tables?'" adds a tetchy secondary school teacher. "Schools are competitive enough among themselves, without the rest of the world joining in over the canapes. Something else that drives me mad is when people say, 'Oh, you have such wonderful long holidays, lucky you.' I feel like getting a badge, I can silently point to that says, 'Yes, I have long holidays, but I spend a good chunk of them working at home.'"

The whole minefield can be neatly avoided by boldly opening up on the topic of the day. "It's quite acceptable to say something like 'What do you think of Tony Blair?'" says Drusilla Beyfus, author of Modern Manners (Mandarin pounds 6.99). "The old principles of no politics, sex or religion have moved forward in most circles."

But watch the other person's body language. If they are not politely nodding and smiling, you may be defending Harriet Harman to a staunch socialist, or putting the case for cannabis decriminalisation to an anti- drugs campaigner. "It's not acceptable to show strong signs of disagreement, such as wide open eyes or head-shaking, with someone you don't know," says Susan Quilliam, author of Body Language Secrets (Thorsons pounds 6.99). "So, if people are uncomfortable with the subject, you will see them go very still - almost stone-like. They might make a move to shake their heads and then control it." The situation is salvageable, she says. "Ask them what they think and let them get involved. It's better to start a discussion than stick to bland subjects."

And what if no-one wants to talk to you at all? One of the key party skills, says Beyfus, is to be comfortable not talking. Standing looking terrified or dejected is a sure-fire way of making everyone else avoid you. An alluringly Sphinx-like air is more attractive. "Look as if you are musing," advises Beyfus. "Be quite serene and stand with your glass surveying the scene, with a half-smile on your lips."

If all else fails, the traditional method of knocking back a few glasses of champagne as a conversational lubricant is tried and tested. And if one should happen to tip over into incoherence, which can happen to anyone at this time of year, at least any gaffes will be unintelligible.