Crossplaying is when you cosplay someone of the opposite sex. or gender. Now Cosplaying in general is when you dress up in a costume or outfit to be or act like a character. Cosplay literally means Costume Play. Crossplaying goes for both genders. It means, if to say, you were a guy and went to a convention dressed as Mikasa Ackerman, that's crossplaying.

A casual invitation / threat used by an individual that is not afraid of fucking someone up.