A beligerent that so completely outclasses their opponent that they can inflict existentially threatening losses with so little effort that its expenditure is indistinguishable from normal overhead

Alternatively, when Stitches managed to ambush your level appropriate character alone in Duskwood

It's from online gaming. To stomp means to defeat soundly/easily. To ROFL is to roll on the floor laughing.

To roflstomp is to defeat someone so easily and completely that it becomes so comical you'll be ROFL.

Downvotes? How strange.