I've often wondered it myself. I feel I get into trouble if I'm just a little confrontational about something. It's like I can't be grumpy or upset, I have to submit to someone else.
And, say, if I'm online or with well trusted male friends, they treat me as male. And I find if I'm indulge in being blunt or making fun of someone like we often do to everyone, no one cares. However, if I'm around people who see me as female, I'm seen as a jerk.
I'm not sure 100% if that is the case, however I can see it being a reason. It's rather annoying.