To be beaten to death by a large black rubber dildo.
In the movie Lock Stock and Two
smoking barrels, the character Hatchet
Harry, beats a man, suspected of stealing, to death with what happened to be at hand.
Harry, also a porn shop owner, happened to grab a big black rubber cock.
This term arose due to the unwieldlyness of the lengthy phrase "He was beaten to death with a large black rubber cock..." and was shortened to simply, "He got gonked."