Spirited Away. I was only like 7 years old when I watched it at a sleepover or something, and I fell asleep fairly early into the movie. All I really remember is the part where the girl's parents turned into pigs, and then the girl herself started to fade and disappear, and then some guy told her to eat a berry or something to stop her from disappearing. And it freaked me the hell out, especially the part about the parents turning into pigs. O_O"
I didn't even know what the title of the movie was for a long time, but, when I did come across it again, I refused to watch it for a good chunk of my childhood. Even though part of me sort of knew that the only reason it scared me so much was because of how young I was and I'd probably be fine if I watched it when I was a bit older... I was still too freaked out to give it another chance. O_O
More recently, I've been meaning to watch it, seeing as how I've pretty much grown out of my fear of it, and everyone says it's one of the best movies ever and all. I just... haven't gotten around to it yet. >_>