We wake up the morning after the night before, head aching, throat parched and we say: "Oh no, did I, did I really, really?"
Chances are, yes, we did. And if we can scarcely remember the details of the office party, there are those who remember the minutiae of our indiscretions, our high spirits, our - shall we say, colourful - behaviour. The restaurateurs.
"My worst nightmare was in the Back Street Cafe, in Bangor, when a company booked a table for 18 and the guy phoned me up on the day saying he didn't like our Christmas decorations and could he put up his own. I said I'd rather he didn't but he said `this is my staff outing', so I let him," says Blackwood Golf Centre manager and long-time restaurateur Richard Gibson. "I came back at 4.30 p.m. and he had put up little trees like the ones lorry drivers have on their dash boards, and he'd wanted extensions and things to light them all up, and this corner of the restaurant just looked like a supermarket on a bad day.
"Then they all ended up wearing them on their heads anyway - and they looked bad enough on the wall. My theory about Christmas decorations in a restaurant is that the chances are someone's going to end up wearing it."
And if there aren't Xmas decorations on the wall for the party animals to pull down and crown themselves with, don't worry.
They'll bring their own.
"The current trend is for everybody to chip in a few quid and to buy novelties," says John Coleman of Popjoy's in Terenure. "And, of course, they are always rude novelties, and you find after a while that people are running around with things on their head that they shouldn't have on their head."
Then, says Ray Hingston of Dublin's L'Ecrivain restaurant: "People bring and open up their Christmas pressies in the restaurant - one man was given a blow-up ewe, and it was all very difficult because you can't exactly go up to someone in a festive mood and say `Excuse me, sir, please take your blow-up ewe off the table, there's somebody behind you trying to eat lamb!' "
Why do we behave like this? This is the question the restaurateurs must ask themselves as the season reaches fever pitch. The reason is simple: alcohol. "People drink more," Hingston admits, "but they are also a bit more relaxed. It's all very good natured.
`The crunch times are all the Friday and Saturday nights throughout the end of November and December. People know they don't have to work the next day. If you're lucky, they'll go on to a night club, but people regularly end up here until 6 a.m. The worst is if they come down at 5.30 a.m. and say `Can you call me a taxi?', and then everybody has to wait for at least another half an hour!"
And onwards, then, into the wee small hours, and, suddenly, it's the next morning.
For some customers, the remembering of the night before is all too much, as Hingston points out: "We have had a few occasions where a regular customer goes overboard at the party, and then never comes back - which is a pity because the restaurant loses out."
According to Ken Buggy, of Buggy's Glencairn Inn, in Waterford: "It doesn't matter how badly people behave, for the next time you see them you won't recognise them - because on the night they all look ravishing."
Buggy puts this down to the fact that people want to show another side of themselves to the crowd they otherwise see every day in office wear. But, if it's very definitely best appearance for the Christmas party, it is, equally, worst behaviour. "It's a nightmare time. The mob instinct takes over," says one Dublin city centre restaurateur so disgruntled he did not want to be named. "If you have a party of 50 they believe that because they have the numbers they can do what they like, and it's very hard for tables of twos in the restaurant.
"The worst behaved are actually teachers and school parties - we've had teachers steal the toilet rolls, because that's their idea of fun.
"The only time we ever laugh at Christmas is when we're on the way to the bank," said the disgruntled restaurateur. But the reality is described by Richard Gibson: "It's quiet in November until the monthly-pay cheques come in, and it's dead in January and frantic in December, but if you level out the total for the three months, it is the same with a lot of extra heartache."