I use the girl's bathroom, even though I pass as male very well (but people think I'm 3 or 4 years younger than I am). I associate bathrooms with SEX, not gender. So if anyone questions me, I'll drop the pants. HOWEVER, I've been kicked out of girl's bathrooms. I even had a man grab my shoulder and point to the man's room, implying I was going the wrong way. Guys seem open to me being in there, because I pass as a guy.
I say pick the bathroom that seems the SAFEST. Are girls going to beat you up in the girl's room? Or will guys make advances on you in the men's room?
I don't use men's rooms much because everyone knows me as a girl... My feminine name is well known. I hope to get a name change...
