Thinking about bad people (thrill killers, rapists) being in agony gets my spiritual dick hard, if we ever get gladiator matches again so I can see some dirtbags skin stretch and tear before his guts leak out while he screams I'd be pretty cool with it. Watching some sick fuck like Gacy go into panic mode while hungry dogs ripped his genitals apart would be fantastically thrilling.
It's not enough to fist rape them, or anything like that, they need to become known, and understood, their fears uncovered, their traumas unearthed, and then used against them. A completely custom experience for each monster.