Abbreviation of the popular nickname for a girl. Stands for "Roast Beef Curtains." Typically comes about after repeated abuse, baby bearing, fisting, taking a black cock, or a violent shocker from a boyfriend that gets carried away. Used to describe a woman with abnormally large and grotesque labia minora. Literally resembles a rosy, beefy, draping curtain.
I tried to have sex last night, but her RBC fell below my sack.