By disturbing I am thinking that you mean something that you see and it stays with you for a long time and alters your behavior. Mine all happen to have an element of horror associated with them...
#1: Dead Again - I was convinced that every person in my life was someone I knew from a previous life who was trying to get me back
#2: An episode of Steven Spielberg's Amazing Stories where everytime the guy looks in the mirror he sees someone trying to kill him... My parents had just put these mirrored closet doors in my bedroom and I couldn't look in the mirror for months.
#3: Arachnophobia: Spiders! What more needs to be said.
I saw Arachnophobia at a young age and it scared the crap out of me. My dad use to have me crawl under the house for random reasons, Ill never be the same.
I saw it in a film studies class during undergrad. Contextually, in terms of the criticism of Italian facism, the film is very interesting but it's still very, very disturbing. I believe Pasolini was murdered shortly after the completion of the movie.
for me it was what lies beneath. It was really disturbing for me to have my hero harrison ford be the killer. It had a wierd effect on me after leaving the theater.