yeah, I know what that's like. just put on a hard shell so that they can't hurt you. it helps, but it's also harder to get to know people when you're afraid that they will hurt you, you know what I mean? It's hard for "bad" people to get to you, but it's also harder to let "good" people in.
While on the topic - here's a song about that(roughly translated from swedish);
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People are dangerous, they bite
Say, were you aware of that?
My neighbours bite
And that old woman too
And the chick next to me on the subway
She bites like hell
People bite!
People bite!
People bite!
Sometimes, more or less
When you're drunk it's okay
But when you wake up in the morning
It gets worse every day
Then their eyes bite more and more every day
People bite!
People bite!
People bite!
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Heh. nice, isn't it?