Backside Brownie Share definition Flag To press against one another, anus to anus, while one person poops into the other's asshole. Man I got so drunk last night, I don't remember shit! People are saying I gave this one chick a Backside Brownie!!! Backside Brownie by thewatermoccasin June 15, 2011 0 0 Get merch Get the Backside Brownie mug. Buy Now — $32.95 See more merch