BMFB Share definition Flag Accronym: Boo Motha Fuckin Boo She's walking like she has a stick up her ass. BMFB!!!Her hair looks like she got electrocuted. BMFB!!! BMFB by bmj05 October 7, 2011 0 0 Get merch Get the BMFB mug. Buy Now — $32.95 See more merch