Definitely
The Crying Game. That completely freaked me out & I got very pissed when it dawned on me what was going on. I almost wanted to puke at the same time that the main character was puking.
The whole torture scene in
Reservoir Dogs in the warehouse, that ear scene made me cringe.
One that stands out vividly in my mind is
Night of the Living Dead, or maybe it was part II. I was a young lad of 8 and my Dad let me watch it at a drive in theatre.
The cute blonde chick is hiding from the zombies, and suddenly a hand punches through the wall and grabs her hair, and begins pulling her slowly toward the wall that has a very long splinter that the closeup captures going into her eye. I did get to see boobies in that movie, so it was a worthwhile trade for the nightmares in my young mind.
There was another movie that I can't remember the name of, it had Rip Torn in it & was on HBO in 1983. There's a big gunfight down in Texas somewhere, and the bad guy is standing on the other side of the car from Rip Torn. Rip ducks down beneath the car and sees the bad guy's feet there, and shoots one of his feet with a 12 gauge. Of course, the foot getting destroyed was in slow motion. For some reason, that scene really bothered me too, to the point that I felt slightly sick to my stomach and couldn't finish watching it.
Most recently, the most disturbing scene was
Passion of the Christ. I simply wasn't able to watch it anymore. That flogging scene was horrific.