I feel the same way, I get extremely panicked when confronted with groups of people, teenagers or men in particular. I have to distance myself as much as possible, I feel as though these are the people who will be cruel to me. I have real trust issues with teens and men who are likely to be sizing me up sexually (I'm a 19 y/o female). Not entirely rational I know, but it's how it is.
I've had a few positive experiences lately that should work toward taking the edge off that, though. Had a pair of 22 y/o male electricians come to work on the house here, and as they left I was expecting them to say something nasty amongst themselves. Instead I heard them discussing how nice my father and house were. (!)
My friend I were searching for her lost cat last week, and she stopped to ask some teenage girls if they'd seen anything. They passed the house again on their way back from wherever they went, and I was surprised to hear them talking about possible places the cat might have gone. They couldn't see us sitting under the tree, so that was nice. Looked like typically nasty girls!
And when we finally discovered where the cat was, it turned out she had been rescued by a young man who had been working really hard to bring her back to health and find the owner.
Goes to show how our minds work against us, but isn't it cruel how one slight reenforcement of our negative perceptions of things no matter how trivial can go toward trashing weeks worth of positive behaviour?