Who Was Worst Dressed at the Costume Institute Gala?

The red carpet at last night's Costume Institute Gala was full of amazing looks, and we can't get enough of looking at all the gorgeous gowns. As usual, though, a few outfits fell flat. Sienna Miller and Jennifer Lopez are currently tied as your picks for the evening's best looks, but tell us — who do you think was the worst dressed at the Costume Institute Gala?