named for the megalodon, it is used to describe injuries that were accidentally self inflicted. like shooting a hole in your hand while cleaning a pistol, or slicing a chunk out of your thumb trying to whittle a block of wood.
guy1- "I mega'd my hand yesterday"
guy 2 "how did that happen?"
guy1- "there is a reason lawnmowers have that "dont put your hand in here" picture on them"