one of those? you might want to include the link next time. i've never cast one though, but karma will usually work by itself, so if someone stole your date and you want them to be hit by bad karma, it will happen. you might want this person to be hurt somehow, but karma might make them fail a test. what you feel would be the right punishment might not be the same as what the universe feels is right.
i suggest you let whatever it is go and trust that the threefold law will work on its own. if you feel this person needs more of a punishment, the try a hex, but you will feel negative effects of karma yourself, so be careful what you wish for. meditate and think about it before doing anything.