Ass Mattress 

Used to describe a person when "Asshole" just isnt enough

Jhonny: Fuck you
Peter: well fuck your mom!
Jhonny: Well you're an Ass Mattress

Ass Mattress by EvetscipE February 14, 2010

mattress ass 

The flattened, unappealling shapeless, but sometimes square rear end of a man or woman. Lacking butt cheeks.

Tush, backside, dumper, arse, noassatall, buns, shitbox, fartbox.

While Peggy has definitely got it going on back there, poor Hank is sporting a mattress ass.

mattress ass by Kel-Kan March 15, 2016