Don't be sad, anon! I play AC:R multiplayer all the time, with a very feminine gamer tag and always trying to choose a female character, as well as a female avatar and, well, being female. Only once have I encountered anyone particularly rude.

In my experience, most of the people in the AC multiplayer are nice. You get the occasional dick, but most people don't talk. Of those that do, I've encountered just as many people who apologise for killing me or congratulate everyone on a good game as I have of those who are arses.