Korn Twist
Fifty headache inducing seconds of Johnathan Davis sounding like muttley being strangled.
Loooping it for hours would be absolute hell.
Or, alternatively you could loop nearly every single Grindcore, Death and Drone Metal song ever made (like sunnO))), Waking the Cadaver, Cannibal Corpse, Job for a Cowboy ect), and any "Normal" person would want to commit suicide in just five minutes.
I personally can't believe some people actually like listening to that shite. In my opinion, It's much worser musically than most examples here, yes even Miley Cyrus, and I'll even say that with no irony whatsoever. At least Miley Cyrus's music sounds human enough...and not like a squealing Pig, or Darth Vader with a throat infection.
Happy Hardcore is another genre that would make perfect torture music, it's literally pop music cranked up on a synth to sound like Alvin and the Chipmunks, nearly all of it is god awful.