I wouldn't call it sexism. Sexism is a belief of gender superiority. What you and your walking breathing retard bait are experiencing is a phenomenon called the "Dude Wank Factor." Its not really your gf's fault or the people hitting on her. Its derived from the idea that girls doing guy stuff means she is actually relatable unlike moat women, and therefore considered attractive. This same concept can be applied to women in military uniform, uaing a firearm, playing sports, etc. What you witness is merely an attempt, albeit terrible, to relate to someone who is psychologically foreign, since for the longest time video games were reserved for the socially challeneged male cliques you knew in high school.