So I was just watching Ai Yori Aoshi, which btw rocks, and anywayz, there's the main char Kaoru and then a bunch of girls who fight over him but are generally too embarassed to do anything about liking him (shut up, it's better than it sounds). anyway, so they go to a beach and meet a new char (chika) who also likes kaoru (surprise, surprise). anyhow, the girls fight over kaoru but get nowhere with him for 2 eps at the beach, and then when they're leaving (without chika), chika runs up and kisses kaoru on the cheek. the other girls get mad, of course, but IMO basically chika owned them.
anyhow, the point is the observation that this was a socially acceptable thing to do. but if it was a bunch of guys after one girl (already sounds potentially kinda bad), and one *ran up and kissed her* on his own initiative without obvious consent, that is very much *not* socially acceptable.