Jurassic Park for me. I had an amazing JP jumper when I was like...maybe 6. It was far too big for me but I loved dinosaurs. Naturally this meant I wanted to watch the film because...well I'm 6 and it's got dinosaurs.
Ultimately I ended up watching it with my Mum and Dad. We got as far as the iconic T-Rex chase scene and I told them to turn it off. Didn't go near the film for another few years.
I've now got my own 6 year old. There's no scenario I could envisage where I even consider letting her watch a film as gory, tense and frightening as JP.
Didn't really mess me up but I watched Fear and Loathing when I was like 12. My friend recorded some shitty Wesley Snipes movie off Sky movies and insisted on loaning me the tape. I watched it once and can't even remember it. But Fear and Loathing was on after it and that movie blew my mind. I ended up taking a shit load of drugs as a teenager. Probably wouldn't have made a difference but I do wonder if that movie left me more open to trying them at the time.