Not necessarily a terrible guy but one lacking in judgement and impulse control. and as such is selfish. He has a couple drinks and " this is what I want to do so I'm going to do it...this second I don't care about the harm I cause...if I get caught I'll say sorry and claim alcohol got the best of me.
You said you got to breath a sigh of relief after your family left. Was the stress generated by " Mr fingers" or other some of the other guests?
I thought you didn't actually know if they saw anything or not? Over the years I've seen plenty of stuff at parties I wouldn't necessarily want to talk about the next day.