You could always beat him up when he's sober - that would be a lot more satisfying. I guess sometimes it's better to let things lie, but a lot of the time you need to respond to show that you're not gonna take it. The thing is, you knew you could take the kid anyway, and the most important thing is that he knows it as well and doesn't start in future. I'd say...let this one go...but if he starts something again then introduce his face to the floor. Letting something go because it's pointless is one thing, but you don't have to take behaviour like that. You sound sensible enough to not get into pointless fights anyway.