Post your favorite torture techniques, for either interrogation, revenge purposes, or just shits and giggles. I'm sure the creative minds on Bad Ideas won't let me down.
Force them to stand naked, with a collar around their neck and a ball gag in their mouth. Take pictures and tell them you will be sending the pictures to their friends and family. It is prefered that you actually go through on this promise, but just the thought of it will make them piss themselves.
Also shop nude pictures of them so it appears as if they are having gay sex with various celebrities.
Blast Death Metal or Harsh Noise so they don't get any sleep. If you feeling especially sadistic you can substitute the Jonas Brothers instead of Death Metal as well. One technique used by US soldiers in iraq was to turn on bright lights every 15 minutes to wake them up, I suppose that would work as well if you don't happen to have any death metal lying around.
Have your girlfriend dress up in a nurse uniform. Have her rub his cock and get it hard. When it's erect stick a mercury thermometer in there and break it. This will get glass and mercury in his dick, which is not very pleasant at all. If it's a girl make sure you rape her before sticking it in her vagina because you won't be able to with glass and mercury in her pussy, unless you're into that kind of stuff.
Shave all of their hair including pubic hair.
Keep the temperature of wherever you are holding them in one extreme or the other. Always very hot, or very cold.
Cut off his fingers one at a time. After you finish that go for his eyes. Nothing strikes feer like a knife going in your eye.
Hold his eyelid open and drip hot wax on his eyeball.
Boil water and when it's hot pour it on him. Bonus points for genitals.
Cover his eyes with duct tape and then after a while rip it off in bright sunlight.
Rip off his fingernails with pliers.