It happens, when people get drunk and they are so close enough to touch somebody... it happens a lot.
I remember visiting another firm during their Christmas party a few years back and one of their low level employees, really a young kid, got so drunk that he started hitting on the boss's wife, I kid you not, this kid was young and he never had a girlfriend before- his boss broke his nose and fired him the day after. lol. That was pretty stupid and hilarious all at the same time.