Or often called "double noggin knocker", is a combat move used to take out two assailants simultaneously. Not to be confused with a headbutt... this move is performed by taking the heads of two opponents and cracking them together, with little impact upon oneself.
You see this kind of thing alot in tag team style professional wrestling.
This move seems less effective against pacific islanders, as apparently, their heads are harder than most people's.
Bushwacker Bob made a big mistake when he tried performing a double noggin knocker on the Samoan brothers.