The action of defaecating into another persons anus, and then them attempting to defaecate back into the original anus. So named because of the extreme difficulty of, how do you say, "two way communication".
Darren: "Dude, I caught Mike wormholing Katie last night"
Cletus: "Really? how did it go?"
Darren: "It looked like two platypusses mating witha chainsaw"