My brother outed me to his mate a guy I know only casually and initially I wasn't too fazed but the more I thought about it the more I thought that he had no right to do that.

Part of the problem is that I found a few days later that whatever he said to this guy it was enough for him to get only a tiny bit of what was going on.

I gave my brother a gentle "serve"

over doing it and I could tell as it dawned on him what he had done...he was highly apologetic and embarrassed. Anyway it s too late now the guy hasn't been around for a week or so but I guess I will eventually get to straighten him out.
You are the only person who has the right to make a statement or out yourself about your gender. It is no one else job apart form yours and makes getting the correct message out there difficult if you are being undermined by well meaning "friends".
Regards
Sarah T