*Cue a billion blogs and articles telling you how to prevent normal human behaviour.*
I'm not going to tell you how to control the behaviour of merry employees.
I'm not going to do that because:
1. You can't. They are people with beer and party hats, and by nature unpredictable. The presence of karaoke may also be a factor.
2. You need to trust them to behave themselves. If you don't, why do you employ them?
3. They are not children. They are perfectly reasonable adults. Karaoke aside.
4. They work all year and like to cut loose a little. Especially if it's the one time of the year they get to do it on company time and money.
5. Drunken stories and moments of genuine personal connection swapped at these events can often lead to clearer understanding and better working relationships. Those "You're my best mate, you are" drunken declarations can hold some water come daylight.
6. They sort of want to keep their jobs, so generally have a lovely time and don't create mayhem. Or they don't do it so obviously as to be found out or create real mayhem.
7. They want to have a lovely time and not create mayhem. I mean real mayhem, involving the scanner, a stuffed badger and custard.
8. The old horror stories of fights over work issues and Jim from Packing and Sally from Accounts being found having sex in the stationery cupboard are largely rubbish. Idle gossip, on the whole.
9. It's meant to be FUN.
10. You are not a sponge there to soak up any FUN that may leak out.
Relax. Communicate the party details confidently and show people you're excited to let your hair down a little too. If they feel it's a positive thing and time and care is being taken to organise it, only the biggest fool would abuse that and behave badly. And at least you'll know who the biggest fool is in your business come January.
So HR people, take part and party. You've earned it too.