Personally, people have asked me about torture before because I seemed pretty good at it in roleplays and such. If you have no qualms about it, you could eat someone slowly in front of them, cut little slivers off over time and then eat it in front of them. But the best form of torture, is to not actually physically torture them. For example, torturing a loved one is one of the best ways to truly torture someone as they are forced to watch and are powerless to save the other.
Personally though, physical torture is more interesting especially when you have time to prep for it. Like opening someones skull and messing around with their ocular cords, putting a small amount of weak acid in their bloodstream(or anything else that would cause pain), forcing them to watch as you dissect their genitals and other stuff along those lines. Though, what DeathWraith proposed is pretty fucking awful(in a good way in relation to the torturers point of view), though I suspect their mind would shut down from that eventually.
And no, I am not a cannibal torturer who chops up peoples jiggly wigglies for kicks.