After her much buzzed about Diamond World Tour concert at the Barclays Center in Brooklyn on Sunday, Rihanna hung out backstage with her famous friends, including models Georgia May Jagger and Cara Delevigne. Rihanna dressed down but still looked glamorous in a DKNY for Opening Ceremony t-shirt ($145) and a baseball cap worn backwards. Adding a bevy or bracelets and killer curled hair, the Barbadian beauty illustrated how effortlessly glam just a t-shirt can be.