Return to Oz came out in the mid 80s. I saw it as a child in theater. Yeah not a great idea.
Poltergeist freaked me out as a child too with the maggot infested steak and guy pulling his face off.
The original Texas Chainsaw massacre also one that sticks with me.
Terrifier as mentioned because it's just so graphic.
The Audition (1999) is another one of those ick movies.
I love the original Saw as the concept and ending were so original at the time it came out.
Another nod goes out to The Platform for originality.
Last but not least I also love Train to Busan as it's so much more than just a Zombie film.