L.M.F.A.O. Share definition Flag an abbreviation for saying: LAUGHING MY FUCKIN' ASS OFF HAHAHAHA. that was very funny. L.M.F.A.O. L.M.F.A.O. by Diego Delgadillo November 11, 2006 0 0 Get merch Get the L.M.F.A.O. mug. Buy Now — $32.95 See more merch