butt curl

The rapid and completely involuntary inward contraction made by one's anal sphincter muscle in response to something abhorrent, unnatural, or just plain repulsive.

Mom left her used tampon in the toilet and forgot to flush, dude! Totally made my butt curl when lifted the lid.

trash humper

A person who gets off on filth, the dirtier the hornier.

When I realized I liked the rank, sourmilk musk of Conrad’s balls, I knew I was a total trash humper.