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1.
Used when you want to say that you would masturbate to something. Usually used be geeks because they know that they have no chance of actually having sexual intercourse.
Geek 1: Check out this picture of Jessica Alba!

Geek 2: I'd fap that!
by painful's mom September 30, 2008
 
2.
Similar to "I'd tap that"
Used to indicate that you would fap to what you are talking about, acknowledging that you have no chance of getting with that person.
guy1: "damn, check that girl out."
guy2: "no way man, she's way outta your league."
guy1: "I know, but still I'd fap that."
by hi im stratton June 08, 2011