When something turns you off so much that you get a negative boner which then comes out your ass. Or when something turns you on that should not causing you to get a negative boner which then comes out your ass.
"man, i saw these half naked pictures of harry potter and got an ass boner"
The act of someone doing a poo, or the poo is slightly poking out the bumhole.
It is called a Ass Boner as the poo poking out your bum is like your penis getting errect.
