sfg Share definition Flag Sfg= Slut Face Gremlin. This is most often used on Aim for someone who looks like a Slut Face Gremlin or who is acting like one. I dont like you because you look like a god dam sfg. sfg by BenjaminT May 22, 2006 0 0 Get merch Get the sfg mug. Buy Now — $32.95 See more merch