"I can be fairly vengeful by nature if I don't keep an "eye" on things... and I like to be reminded once in a while that I don't have to reciprocate all the time"

That sounds like me. I can only think of one situation though, where I was secretly vengeful, because so much stress/hatred had been forced on me. Until that secretly vengeful moment, I felt like hell for months. I must be a little evil. ;)