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
by EvetscipE February 14, 2010
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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.
by Kel-Kan December 8, 2015
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