So to return to your example, the girl in the dress is wearing a purple dress.
Prior to that point, the Fe-dom female in the group has through various means indicated the inferiority of purple dresses. She has shared anti-purple dress article to the group from Vogue, expressed her belief that people that wear too much purple have delusions of grandeur which she can't stand, poked fun at Angelina Jolie for wearing purple again to a movie premiere ect. And because everyone already thinks that Fe-dom female is cool/down to earth/worldly/ whatever, she's listened to.
Thus, when girl wanders in that whorish, self-involved and ugly purple dress everyone will roll their eyes. She hangs out, then leaves and almost immediately one of the girls she'd just been chit-chatting with turns around and says "What was she thinking wearing that hideous thing?" and the Fe-dom will very charitably turn around and say, "I know, but she's our friend and we shouldn't talk about her like that. It's so catty."
I'd say we hunt 'em down and burn them like witches if I didn't know it would make my romantic life so hopelessly dull.