252+ Atk Life Orb Bisharp Knock Off vs. 4 HP / 0 Def Mega Houndoom: 81-95 (27.7 - 32.5%) -- guaranteed 4HKO
Losing a third of your health and a weakness to sr isn't pretty, especially if you no form of recovery.
It's not pretty but at least you don't lose your item. Only those with Mega evolution can take the risk of switching into a knock off while avoiding losing their item, and out of all mega's I'm aware off, only T-tar, Mawile and Houndoom resist dark attacks.
Knock off is really an ugly move to face, especially if your team depends on knock-able items like I do.