I do not handle rejection well myself. Even here on PC, when I post a thread and almost nobody replies, I start to feel rejected and rotten.
For me, it has to do with my upbringing, especially by my father. It was either do something perfectly and be grudgingly accepted, or fail and be either totally ignored or beaten up and/or be diminished to dust with sarcasm.
I still find myself trying to do things perfectly (which in itself is vague and unreal, I know), just in the hope of being acknowledged, being allowed to exist. And as soon as I think I fail, I want to stop and run away.
So when people reject me (or something about me), I feel like I have no right to exist.

The head knows better... the rest of my still freaks out at any sign of rejection.