Computer slang for "peeing in my pants". When lol, rotfl, or lmfao just doesn't convey how hard one is laughing, pimp takes it a step further.
See also: lol,rotfl,lmao,lmfao
Dave: Why did Tigger stick his head down the toilet?
Steve: I don't know....why?
Dave: He wanted to see Pooh
Steve: PIMP!