Fack Mather Share definition Flag Oftenly used in SRO, is an slang term for Fuck Mother. Guy1: Dude, get the f*ck out of my grinding spot. Guy2:Fack mather! Fack Mather by MetalMasteR™ April 19, 2009 0 0 Get merch Get the Fack Mather mug. Buy Now — $32.95 See more merch