It's a piggy back ride but you hold onto the booty instead of their legs
Do you want me to give you a booty back ride?
(A sexual act) A guy gives a naked girl a piggy back ride whilst her pussy rubs up and down his bumpy spine.
“Dude I can’t believe that he gave her a Pussy-Back Ride, I didn’t know that they were freaky like that.”
“I heard he gave her a Pussy-Back Ride if you know what I mean…”