Young men see online gaming as their last bastion of unchecked masculinity (or at least the half-formed idea they have of it). A girl "intruding" on their "sacred field of battle" threatens them; they run the risk of being beaten by her, someone perceived as inherently weaker. This is their nightmare scenario- a woman being more "manly" than them, thereby consigning them to being "girly"- and to a group who values themselves solely on shallow displays of machismo, this is a devastating blow. Therefore the young woman is unwelcome to them and must be chased away by the one means of attack they know- incessant, loud, foulmouthed insults.
Either that, or they're just jerks.
