Why do boys act so nasty?

There is plenty of guys at my school and all they want is one thing, but I wonder why are boys like that???

boys act like that infront of others because it makes them seem more of a man...
they want others to see that they like girls and it makes them sound like they're not virgins... which by the way many of dirty minded guy are!
it gives guys the feeling of fitting in with others... I mean, hey, what else can they really talk about other than hot girls, sports, games, and food...