Obviously these folks should just avoid the crowd or go to concerts that have a vibe they actually enjoy, but it's not weird to be upset when someone, accident or not, hits you multiple times/pours beer on you/etc (especially when it's made clear to them that "hey, you swinging your fist around kinda hurts."). Accidents happen, crowds get really cramped, but it's usually considered courteous to be at least a little aware of where your limbs are going. It's a 2 way street: you hit someone and they acknowledge it, maybe be a little more careful. Someone's fist falls on your head, maybe remind them you're right there? It's not that hard. No matter the size of the concert though there's always gotta be at least 1 asshole. Haven't been to many with an invertebrate in the audience though.

All that being said, going to the manager is pretty fucking funny lmao. Just move a little further away from the stage and enjoy the show. You really can't expect people to not spill in a crowd, or bump you, whatever, when you're standing elbows to assholes or whatever the saying is.