Top definition
Stands for: Poke My Belly Button.
If you poke your belly button, your bum falls off.
Used as a less vulgar version of "lmfao."

Derives from eccentric grandmothers who use obscure terms.
#1: Oh PMBB!
#2: Okay.
#1: <bum falls off>
by rachebjacol November 05, 2009
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