The unsightly view of a woman's rung out, stretched out, flappy, vagina lips. The name was chosen because it resembles what a curtain of beef would look like.
Ex. "Omg, Did you see the beef curtains in between that girl's leg?"
The act of pulling your pants and underwear down, then letting a nicejuicy mud monkey slide out of your anus into your unknowing friend's or sibling's mouth.