February 11, 2012 - Larry Busacca/Getty Images North America more pics like this »
Girl on Girl

Given her natural assets, Katy Perry is probably used to being stared at in the chest region, so you'd think she'd know to keep with the eye contact when talking to an attractive woman. But even Perry couldn't look away from Rihanna's hot bod in an extremely low-cut black dress. Yowza!