A "reverse euphemism" is a euphemism that works in such a way as to poke fun at most euphemisms. For example, a euphemism for beating up freshmen is called a "hazing." A reverse euphemism for a place where freshmen were being beaten up would be a "genocide convention."
Bob: Oh, hey, school just let out and it's YMCA night, so I've gotta go take a shit.
Bob: I mean I actually have to drop the kids off at the pool. Haven't you heard a reverse euphemism before?