Justin Bieber -- Don't Laugh at Me ... I Bang 'Bitches'

Justin Bieber bragged that he f**ks "bitches" in a desperate attempt to save face after he got ripped to shreds during a comedy show in L.A. -- and TMZ obtained footage of the entire awesome display.

Biebs made a surprise appearance at the Laugh Factory on Friday -- during comedian Chris D'Elia's set -- and the ex-"Whitney" star ROASTED Justin for his ridiculous fashion choices. Douchey genie pants and leather tank top, por exemplo.

Justin sat quietly through the ribbing until D'Elia made a joke about Justin only "f***ing" himself -- that's when JB just had to respond with a quip that was disgustingly misogynistic ... or totally female-friendly.