This one is very easy to answer, "The Entity". I actually went to the theatre lllooonnggg time ago when it was released, early 80's. The fact that this woman is repeatedly raped by a ghost in any part of her home, in front of her children or whoever is around was incredibly disturbing to me. Actually, any movie that depicts a graphic rape scene is quite upsetting.
Kids was definitely one of my more memorable movie-going experiences. The theater was packed, and while the film was running, no one said a word, although quite a few got up and left.
I wish I had a video recording of the audience as the lights came up. Nobody got up or spoke. All just sat there with their mouths agape.
Haven't seen anything like that reaction to a film before or since.
I thought the movie was great. Truly reminded me of people from high school. yikes!
Bully was also a pretty disturbing movie from Clark. It seemed to get a cooler critical reception than Kids but I love both. He lost me with Ken Park, however, which seemed like it was made just for shock value, imo.