An A-Cupper is a woman who tries very hard to get men to notice her, mainly in a slutty way. Similar to woman who sluttily flaunt their A Cup breasts.
No offense meant to real A-Cuppers- women who have actual A Cups.
See also D-Cupper.
Girl 1: Do you see Melissa over there, trying to impress Kyle?
Girl 2: Yeah. She's such an A-Cupper. Whore.