Dirty Crab Share definition Flag Sexual slang for inserting the thumb into a woman's vagina while simultanously inserting four fingers into her anus. Bob: I heard you went home with Cindy last night Jack: Yeah, and I totally gave her the Dirty Crab Dirty Crab by MrDee February 22, 2007 0 0 Get merch Get the Dirty Crab mug. Buy Now — $32.95 See more merch