poop slap bet

A pact that is made by firmly grasping the hand of another with a solid dollop of feces between the palms. After the handshake, whomever loses the bet gets slapped with a similarly smeared shitty hand.

"Bro, I bet you can't stick this pencil all the way into your dick hole."
"....Wanna make it a poop slap bet?"
"You bet your shitty hands I do"