There are a few enemies like the Crypt Guards in Unhallowed Boneforge who, if any melee combatants are nearby, will turn and do a "cleave" to them for minor damage (~4k). However, criticals from this cleave are still modified by Toughness, which your average dps will not be wearing and can exceed 30k. I believe this to be an oversight.

The damage has clearly been toned down so that a melee player takes damage but is intended to survive, but I think the critical damage being exceptional has been overlooked.