Lots of bits in Hobo with a Shotgun. Like when a busload of kids get burned alive. Or when a character has his head dropped down a sewer grate with a rope around his neck, and gets decapitated as a motorcycle, to which the other end of the rope is attached to, drives away. Cue literal fountain of blood and to top it all off, a stripper dancing in it. Or the part where the protagonist gets whacked repeatedly on the back with an ice skate. Or when the female lead gets her arm fed into the blades of a lawnmower. Yuck.
I could also list basically the entirety of the Koroshiya 1 manga, but one bit still sticks with me: the protagonist, having followed the prostitute he has a crush on to her home, sees her get horribly abused and beaten by his boyfriend. The boyfriend then proceeds to violently rape her, all the while the protagonist is still watching. And then he starts jacking off! Yeeech.
Also the chestburster scene from the original Alien is still very intense even by today's standards. The noises John Hurt makes, he sounds like he's about to throw up and convulsing as if he's having an epileptic fit. What seals the deal is the female actor's sobbing after the alien pops out, since it's completely genuine: the actress didn't know the scene was going to be that bloody, and was sent to genuine shock by it.