Quite simply, an adult female who's face resembles, in no small part, a big fat steaming piece of shit.
Look at that fucking ugly bitch! I really can't think of an expression that captures the entirety of the disgust that I feel upon observing her facial features.
Boys who enjoy yaoi (a genre in Japan that contains sexual and/or romantic relations between two men); literally translates to "rotten boy"; corresponding female : fujoshi