A Rotbag is a highly unattractive person, generally female. (see Cabbage Patch )
A Rotbag has a face only a mother could love, and generally works at a radio station or on a night shift to hide their uglyness from the general public.
DO NOT LOOK AT A ROTBAG, YOUR FACE WILL MELT!!!
Dude, look at that Rotbag over there. AAAAAARRRRGH MY FACE IS MELTING!!!!!!!