I play all women characters because I'm a woman IRL. I get SO TIRED of people in groups referring to me as "he". It's really annoying. I know folks just assume but there ARE girls who play this game, including lots of my RL friends who I play with. It's just aggravating.
For me it's irritating when they then "jokingly" (we all know the jokes) refuse to believe you when you say something like "I'm a she." It never used to bother me, in the past I would ignore it or even laugh along, but I guess it starts to wear on you after quite a few years of online gaming.
I just call all male characters "he" and all female characters "she", unless told otherwise.