This is literally exactly the same as casting a curse. The three fold law is Wiccan dogma not a law of physics, so there is not bad karma for cursing. This is not even how karma works. Stop being holier then thou!
14 Ways People Got Great Revenge On Cheating Exes Funniest one says she exchanged her ex's boss' phone number for the bimbo's he was sexting with, another wiped her cheater's tighty whiteys in poison ivy so he thought he had herpes.
10 Ways to Get Revenge on an Ex － Living well is the best revenge, but we can't help but fantasize about whipping out these methods on an ex. We'd never actually do them, but daydreaming about them is way too much fun.