How to make someone's life miserable without letting them know you are doing it?

I'm not saying to be a bully, but give back the crap people give you. How can you do that? I want to see them cry and cry and I want to see me laughing hysterically. How do I do that? I mean I can trip someone but that would only cause physical harm and if I cyber bullied, they can trace my Ip Address which sucks.