Butt-yak 

VERB, An expulsion of flatus during a bowel movement that is powerful enough to throw a heavy spatter of semi-liquid feces in a muddy spraypaint fashion.

I butt-yakked so hard that I got some on the seat!

Butt-yak by The West Side Smasher April 24, 2003

Yak Butt 

Someone with a large ass approximately the size of a Yak.

Dude, that ckicks Yak Butt almost tuched me.

Yak Butt by Kevin May 1, 2006