Superficial woman, usually between ages of 15 & 35, who obsessively follows the fashion dictates of _Cosmopolitan_, tries to achieve that 'perfect' Barbie-body, and thinks of little besides personal appearance. Universally falls into heteronormative trap of objectification, sees own worth as determined by ability to attract men.
Rachel McAdams plays a cosmarbie on TV. Paris Hilton--cosmarbie icon or pinnacle of cosmarbie-ness? Cindy Jackson is perhaps the most literal of cosmarbies.