butt curtain 

when someone ties a sweatshirt around their waist to cover their butt.

When Alyssa and I go walking, she always wears a butt curtain.

butt curtain by lauryn June 5, 2005

Curtain Butt 

a floppy, saggy, generally nasty butt

"What you talkin' about...Curtain Butt? I'd hit that!"

Curtain Butt by SPDRMN October 5, 2006