I'm not one of those guys, but I understand the mentality.
A lot of shooters; whether intentionally or not, or more geared towards the beer-drinking frat boy market because of the violence and not quite deep plot-lines (note: I am talking in generalities here). A lot also can be considered "party games", like Halo and CoD, and the fact that whenever you play online with these games, there always happens to be an obscenity screaming prepubescent child who usually doesn't know what s/he is talking about, thus falling into the generality of a "stupid gamer".
One of my favorite games happens to be a shooter (Area 51, I'm looking at you and your duel shotgun wielding deliciousness), so brand me a "stupid" gamer if you so wish.
I'll be off playing Area 51 if you need me.