Celebs: one week they're totally fab, and the next week they're a total flop! With heat waves taking the country by storm, celebs are breaking out their casual cool outfits and the results are definitely all over the style spectrum!

While Eva Mendes looks effortlessly cool in a flowy dress, Miley Cyrus rings the fashion police's alarm with her mesh bra get-up. Others, like Taylor Swift look simply fab, while Amanda Bynes tries to use her tiny cute dog to cover up her fashion misfortunes.

Click through the gallery to check out all of this week's best and worst celeb style, from Mariah carey to Rihanna to Mary-Kate Olsen!