And your girlfriend is actually your boyfriend and you wore the panties because it makes your little dick hard
Don't be such a fucking asshole. Read the damn story and laugh. My dick is always hard. Do you want to suck my dick but only if you are a fucking woman.
You should've knocked her on her ass, then asked the other girls if they thought that was funny.
Honestly it sounds like your S.O. has a masochistic streak. Some people get off on the humiliation of others. If this is the first time this happened, I would keep your eyes open, or think if they have ever done anything like this before. You could also try the adult thing and talk about it. If this is not something you are interested in then leave. Even if this person is not in S&M, they need a respect check. I bet they wouldn't have liked that being done to them!