This is one of those things, like dealing with misbehaving children that aren't yours, which is a lot easier to do the older you get. Not only do kids, even teens, generally have some sort of instinctual deference to older people, but you just stop caring what 5 random strangers think or say about you.
Grey hair helps. I can't wait until mine grows in.
What I'd specifically do is put on my best Mama voice and say, "Absolutely not. End of the line, or I'm calling security, your choice," and hold up my cell phone. It's like working with animals - don't show any doubt that you're in the right or that you'll be obeyed. Don't ask questions. Just tell them how it's going to be. But that probably won't work while you're a young male.
I...uh...wouldn't have the balls to do it if I wasn't in a crowd, though. 'Cause she really could tear my shit up, y'know.