yea you could get in trouble for it, but serious trouble? Not really. I don't see why this is "immature," if you're pissed off and it's just water not acid, they do a lot worse and he probably deserved it anyways.
edit: Probably has been mentioned but on "Basketball Wives" the guy threw a drink all over his ex wife and next day everyone seemed to think that was funny.
http://www.youtube.com/watch?v=57Cpt...eature=related