An abbreviation for Big Fucking Dick. Can also be used in text messaging and instant messaging.
Jenny is at the movies with her new boyfriend and they start playing with eachother in the dark. He pulls out his Johnson and after playtime is over she texts her best friend Joanna the following "Wow. Like OMG my new guy I met at the bar, the tall one named mark has like a B.F.D. It is like that big"