Imagine a hypothetical situation where someone did something really bad to you. Imagine that this was the worse thing that any person could ever do. Imagine the most detestable thing you can think of. For example, let's say aman murdered your family or something. Whatever this man did; imagine that he had no actual reason to do so. He simply wronged you because he thought it was funny. It brought him joy to bring you to extreme pains. Most might consider him evil or a sociopath. Call him what you want. Anyway, whatever he did, imagine that it haunted you for a large majority of your life. It left you lying awake at night thinking about him. Thinking about getting revenge for what he did. Now, imagine one day, you find this evil man in a quite, isolated area. No one's around. It's just you and him. Now, imagine you have the resources to get revenge in any way you please. What would you?

Most people would probably shoot him, probably with a shot to the head. Some may shoot him in the stomach to leave him in pain. And I think only the most extreme persons would stab him and let him bleed out. I never understood this approach. Using these methods, you would only be leaving this man in pain for a few hours. He would only hurt for a few hours in exchange for nearly a lifetime of trauma from yourself. Why would you kill him? Don't forget, I'm talking about the most evil man imaginable. This is a guy you hate so much, you see him when you've closed your eyes. You've dreamt about making him feeling the same pain he made you feel. Wouldn't you want him to feel as much pain as possible?

That's why I wouldn't shoot him or stab him to death. I wouldn't want him to feel pain for only a few minutes or hours. I would have this guy in pain for years. I would try to keep him alive as long as possible. I would chain him up cause both emotional and physical trauma to this person. I would want him to live so long in my possessions that he forgets what it's like to live in the real world. Essentially, I would put this guy in hell. I'd probably lock him deep down in some secluded chamber and I would torture him everyday (I want get into specifics). I'd make sure I feed him and give him medicine so he stays alive. I'd make sure he sincerely believed that he was going to die one day in my dungeon. And he'd know that day was a long way away. I don't think there's any mental torture as bad as that.

I would make him choose which method I would torture him. I would give him the most disgusting food imaginable; making him decide between starvation or disgusting crap. But of course he'd get used to it and his pain threshold would increase. So every once in a while. I would act like I was going to let him go. I'd open his chamber door and let the sunlight shine through. Then I'd tell him he was free to go. Then, as soon as he gets a smile on his face, I'd bring him back into the chamber and repeat the torture process. Of course, I'd never show him my face though, just in case he got out. And then, maybe after ten or fifteen years of torture, if he's still alive, I'd just let him loose. He'd be so fucked up that he wouldn't be able t function in society. So even though the physical torture would stop, the psychological torture would continue. I'd probably observe every single aspect of his life afterwards and I'd relish in his shitty life afterwards. 

etc, etc

So, if you had the oppurtunity to take revenge in any way you could imagine on the most evil person you could imagine, what would you do?

With no games to play, that's some serious torture right there.

But seriously OP, think about it for a second. If you went through everything you said, like torturing the guy for 10-15 years, locking him up in your chamber, keeping him under constant surveilance, setting him free but still stalking him to gain pleasure from his misery, do you think YOU would remain in a normal condition yourself? I mean yeah you would mess this guy up for life, but you yourself would probably be just as messed up from all the scheming, plotting, torturing or whatever unspeakable thing you may do to inflict pain upon him. So in the end you would never really recover from your own trauma he caused, but you would just destroy him along with yourself.