dumpy bumpy

its somewhere between "dump truck ass" and "cutie booty"

Slang used to describe sexual activity involving oneself's anal cavity especially if the receiver is rather large from behind. Typically the posterior-end is referred to as "dumpy" which is due to roots within the word "Dumptruck" (which is a vehicle commonly used to haul large quantities of sediment from one location to another), and the word "bumpy" being used to describe the motion of anal sex where one bounces off of their partner.