Unionbutt 

An ass so good it makes you cry.

Why are you crying?
Look over there.
Oh sweet Jesus, an unionbutt.

Unionbutt by Prins-e30 March 14, 2014

Onionbutt 

A butt so amazing it brings tears to one's eyes.

Jim: Hey Scoot, you see that hostess?
Scooter: Damn, she's fine and check out that Onionbutt!

Onionbutt by Nefmaster July 20, 2011

unibutt 

your ass looking as though both cheeks are fused together.. causing the look of one ass cheek. it is an insulting comment.

"damn.. look at brooke's unibutt.. that is not a fine piece of ass."

unibutt by Emily and Brooke June 4, 2005