When one pulls out of ass, only to discover a nugget of shit on the end of ones cock. Then one picks it off and throws it at the unsuspecting victim while screaming "SCOOBY SNACK!"
A variation of the rusty trombone in which the man receiving the rusty trombone takes a dump in the mouth of his partner as they are licking his anal hole.
Man, your Mum was gobbling up Scooby snacks last night!