the act of rubbing one's ass in the face of another, should be a surprise attack, and the receiver of the butt wash should have to struggle to get away and be left with a disgusting taste/smell remaining on their face
My roommate was sitting on the couch the other day, and I got up and gave him the biggest butt wash ever. I even left some shit on his upper lip.
Afghanistanian butt-wash is a word where you take your partner to Afghanistan, go behind a car wash, and proceed to have Sexual intercourse while pouring Soap on the Partner's Anal Area.
Ya I gave me wife the Afghanistanian butt-wash for her birthday, and after that she told me that that day was a special day.