Drinking at the workplace is not a recommended activity if you can't practice moderation. But what about when it's Christmas time, and you have to tipple just a little even just to fit in?
Suffice it to say, you're going to get in trouble if you drink to excess and let your lowered inhibitions take you to places you wouldn't go during the normal course of a week.
Best practice is to drink a toast and get the hell out of there. They can't fire you for things you didn't do because you didn't stick around to tell your boss what you really think about those 9:30PM emails telling you what's coming up the next day.