Wild Mouse at Blackpool. It's **** terrifying, rough and not at all enjoyable. (I know I'm on my own with that opinion).
Grand National also at Blackpool. Same reasons really, it's too rough and painful to enjoy.
Stampida at Port Aventura. Rough. Painful. Headache inducing.
Trying to think of a steel coaster. I adore it but Montu does spring to mind because it is really forceful in places, but it is still one of my favourite coasters...probably for this reason. It isn't at all painful like the aforementioned wood.
Can't think of any steel pain. I'd imagine the Smiler would come to mind for some but I haven't ridden it since summer 2013...when it wasn't that rough and really enjoyable.