I haven't been traumatized by any scenes in any movies. However, watching Poltergeist 2 or 3, I think, scared my very much. Luckily, I was an adult at the time I watched it. It is the Poltergeist movie in which there is a really, really bad men singing a hymn 'god is in his heaven' (just for info this is). I was really really scared - of this man. As said, though, luckily, I was an adult when I watched this - meant I could see the very good acting here.
I don't know how many of you know this, but Danish director Lars von Trier made a tv-series called Riget (I think it was redone in the USA under the name: Kingdom Hospital?) In it, there's a ghost, a little girl that has died a mysterious death. And some of these scenes really, really scared me. Again, I was an adult at the time, I watched this. So I could recognize and appreciate the good acting. It is not that the scenes are scary in itself; it is that you never know when they're coming, building suspense it is called. hitchcock was a master in this regard, best seen in his movie 'the birds'. For weeks after watching this (as a teenager, I think) I looked at crows and other birds differently. Later, at university, when we analyzed this movie, I learned what it all was about; however it did take some of the childhood fascination away.
Wwhen I was younger, 12 or 14 or so, my big sister and I were home alone as my parents were away on a business trip somewhere. We saw a tv-movie based on 'the turn of the shrew' by Henry James. And the ending made me and possibly my sister too? very, very frigthened. Luckily, we had each other so that we could about what we just had seen. I think it was called The Innocents -
(source:
http://en.wikipedia....rn_of_the_Screw ) - as it was in balck and white. And the fact that it was totally in B/W just made it more frightening, it seems. It looked so authenthic, did it.
Of course, I did not know this at the time, it is something I've learned how to appreciate and analyze since.
Today's horror movies are nothing like the good old ones as they try to much with blood & gore and other effects. Not effective - what is most effective is to trick the human brain - or to scare us by building up a suspense and then either a) trick us or

release the suspense - but not by letting us see the violence, just a hint of what is going on. Then the mind or brain will fill in the rest. And that is way scarier than anything...