What an ass.

Rihanna looked über glamorous at the Met Gala in New York City Monday, baring her toned midriff in a white look she co-designed with Stella McCartney. The "Monster" singer, 26, added a touch of sparkle with Jacob & Co. and Dionea Orcini jewels. Rihanna spent the evening hanging out with Kate Bosworth, Cara Delevingne and Reese Witherspoon, all of whom wore bespoke looks by McCartney.

Later that night, however, Rihanna quite literally became the butt of the joke.

For her official afterparty at Up & Down in the West Village, the "Pour It Up" singer changed into a slinky gold dress that featured a plunging back. The braless beauty went commando—a move that would later bite her in the ass. While posing for photographers, she flashed two inches of butt crack.