Not exactly traumatising this, but slightly creepy, and that is the fact that one of my friends now has a scar in his arm in the shape of a crucifix, carved by himself. This was back when he was going through a terrible phase of depression, and I'm glad to say that nowadays he's never been happier.
A traumatising thing that did happen to me was that I had gone down to my local subway, had bought two sub-sandwiches for my brother and me, and two drinks, and was heading back to my house, being only a few streets away from it, when I saw two rather disrespectable tall, late teenaged boys, one putting a bandanna over his mouth. A warning light flashed in my head, but my hands were full and I was hoping they'd walk past like everyone else does. Of course, once near, they flung me to the ground, spilling the remaining drink (I'd had the first one earlier) all over. They let me get up, then searched my pockets, all the while babbling about me doing something to their "cousin" (a load of bollocks of course as I was far too weedy to attempt to bother anyone, as proven) getting some shitty change for their efforts, and no phone (I'd luckily decided not to bring it). As a final parting grace, the bandanna-clad one snatched one of the subway sandwiches (which turned out to be mine as well).
Since then my distrust for humanity has become so bad (and believe me, it wasn't good to begin with) that whenever I walk past someone in the street I imagine how likely they are to attack (based on gender, weight, hands-full, being a couple), run a scenario through my head of how they might attack, and brace for impact as they walk past. I always feel a slight jolt run through me if I walk past someone who looked particularly likely and able to strike.
Oh well. I can only hope that guy didn't like pepperoni.