It could also be some female gamers feel as if they don't belong in this type of environment. Going with your "macho competitiveness", some females may feel as if they have to attempt to keep up or lead the pack in that regard so they either work hard or act out. In response to that, some male gamers may feel as though that type of female interaction or "intrusion" ruins gameplay for them hence their acting out. In my generation, I've noticed a spike in female gamers, especially in role-playing games. But then there are those that play shooters and are often tested on not only their skill but ability to act under pressure (hence the competitiveness). When other girl gamers find each other, we either team up or go against each other to prove who is the "better alpha female". So really we don't help ourselves either.