The only rejection line I ever received (coming from my only attempt at dating so far, unless you count a few messages sent on OkCupid as attempts) was actually very nice. In short, she was my friend, I developed feelings for her, something happened that could be interpreted as interest on her part and I asked her if she was interested in me. She apologized for the misunderstanding and told me that what she did was just something she does as sign of friendship. I told her she should not apologize and we should just forget about that and she agreed.
It was probably the nicest rejection in the history of mankind and we kept our friendship intact for the rest of the semester (to this day, we sometimes talk on Facebook, mostly about music videos we both share and my crazy photoshopped profile pictures). Nevertheless, since she was the first (and so far, only) girl I ever fell in love with, it took me three months to get over her rejection. In fact, I have not yet completely gotten over it, since I still sometimes think of what it could have been.
Yes, I am aware of how pathetic I am, thank you very much.
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DISCLAIMER: It should be noted that, while I strongly suspect I have Asperger's syndrome, I am not diagnosed. Nevertheless, my score on RAADS-R is 186, which makes me a pretty RAAD guy.
Sorry for this terrible joke, by the way.