The jumping hippo is when a fat bitch rides you with the cowgirl or reverse cowgirl. This is a very dangerous maneuver because you might snap your dick or break your pelvis.
Guy 1: Yo, I was with this fat bitch and she did the jumping hippo
Guy 2: Bro, are you okay?
Guy 1: Nah, my dick went 90 fucking degrees and it's stuck like that.
Guy 2: Oh shit.