Miley Cyrus Pantless on the Red Carpet

5/21/2012 7:00 AM PDT

Teen pop tart Miley Cyrus spent so much time getting her new hair 'do cut and blown out ... that she forgot to wear a bra and pants under her white blazer dress thing at the Billboard Music Awards in Las Vegas last night.

The 19-year-old's low-cut jacket showed off a new side of Miley.