I'd also have to nominate Son of Beast for this dubious distinction. I rode it when it had the loop and it was the part after that which was awful. It literally gave me a pounding headache and my neck was really sore for at least an hour or more. I've been in two car accidents (one where the pickup truck I was riding in t-boned a car that ran a red light and shoved it under a tractor trailer!) and I swear that and a few other coasters have done my body much worse. Actually bad coasters can be worse since neither accident lasted more than a few seconds, but SOB made me really wish I could have stopped the ride and gotten off. I almost never feel that way about any coaster, even ones that I don't care much for.
Other honorable mentions are Hurler (passed on the one at Carowinds, I didn't want to aggravate my back) at KD, Shockwave at KD (thought I was going to end up with a busted tail bone), Grizzly at CGA (rode it way back in the 90's and it was bad back then), Vortex at the same park (at that time I couldn't believe that a B&M could be a head-banger, but sadly it's not the only one, as I incurred a good Vekoma-esque head-bashing on Raptor this summer), Mean Streak (actually rode it again this summer and it was "rideable" in the front seat; not as rough as I remember it years ago), and Hoosier Hurricane at IB (made the mistake of riding towards the back and I paid dearly for that, my neck ached for close to an hour).
Others too generic and numerous to mention would include SLCs (lots of jittering and head-banging) and most Arrow loopers (the worst of which I've ever been on was Drachen Fire - I should have been forewarned when every other coaster and ride at the park had hour-long lines and this one was a walk-on!).