I have no problem with OOC horribleness of basically any kind, so you're set there--Cain, on the other hand, will likely get really, really pissed at the implication that Riff is subhuman or savage simply because he's a servant. He also has something of a savior complex when it comes to violence against women (although not enough to stop him from pinning them to walls to hit on them despite protestations...), so that might also function as a berserk button for him, depending on how far it goes etc.

Or he might just try to poison Alec's food.