I have only heard the term used once, but I understood immediately what it stood for, because some of my kids' friends insisted on rap music in the old Dodge Caravan kid carpool, with me as driver.  I always said "OK, but the first time I hear "MF" I'm going to change the station to easy rock." It usually took less than thirty seconds, and the kids would roll their eyes.  As a younger man I lived in a black neighborhood and saw just about everything, including a lot of good. But those kid wanna-bees in the back of the Caravan didn't have a clue.