Just to play devil's advocate here. I've meet some people before where I haven't been sure guy or girl, (this was before I had any idea what trans was) and I felt terribly nervous that I'd make them mad. Some people don't MEAN to be presenting as the opposite sex, they just, well, look it. Don't want to insult them. Also seems very rude to not be sure. So a lot of casual acquantences who get your pronoun wrong are probably trying to be as polite as they can, they just don't know better.
I suggest business cards. Or children's books. Or a taped lecture. But yeah you've just gotta educate the hell outta them until people get it together and realize how to treat you.
As for people not believing you...I can come smack them if you'd like.
