step-mother fucker Share definition Flag A man who is a step lower on the social rung than a plain ol' average motherfucker. Brian thought the was a bad mother fucker...but he's worse than he thinks...he's a step-mother fucker. step-mother fucker by DOTK April 1, 2010 0 0 Get merch Get the step-mother fucker mug. Buy Now — $32.95 See more merch