I'm talking about that "no one fucks me over and gets away with it" standard. And the scenario the OP describes is alien to me, since if you wrong me in anyway ...I will immediately point it out and deal with it in that same moment. I don't let it fester inside. And because I don't...there is no such thing as the case of someone consistently fucking with me. Retribution should be served in the moment if at all. Otherwise it's just too machiavellic for my taste.
So I would say the stimulus-response in the OP situation (you are talking about he deals with people that wronged him right?) is not AT ALL direct. If you want justice...serve it swiftly and fairly in an impartial manner. Don't wait for "karma" to take care of it. The world isn't inherently fair, and there are plenty of naive people out there. At least just as many as there are assholes. It's up to each one of us to deal with reality for ourselves.
Just, personally, I try to let go of any sort of less-than-merry thought for other people. I prefer to strengthen myself rather than hope they become weaker at some point. And it's also about trying to defuse hate as a concept in my life and in those whom I interact with. Call it buddhist evangelization if you want