An Interesting American Expression

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May 26, 2012 15:50
Hello guys, recently I was keen on watching Friends VERY much!!! And I have finished watching more than 4 seasons. Today I was confused by a kind of interesting expression, here it goes:

A: see you later.
B: Not if I see you first.

I was told it was a sense of humour by searching the Net. But I can't really understand it well either. So I beg your help, thank you very much~~~

Wish you all guys have a wonderful weekend!