full of herself
From the This is the End trivia:
Initially Michael Cera wasn't really slapping Rihanna's butt, but rather making the motion and stopping right before touching her. As a result, the scene wasn't working on camera because it looked too fake. Eventually Cera asked Rihanna if he could really slap her butt, she said yes but on the condition that she be allowed to really smack him across the face each time. Cera agreed.
she sure is full of herself!