New rule: If your significant other really loves you, s/he will agree to act out your favorite movie. MTV asked Mariah Carey and Nick Cannon to play Rachel McAdams's Regina George and Lindsay Lohan's Cady Heron (respectively) in the "So you think you're pretty?" scene. And Nick did it because Mean Girls, as you might know, is Mariah's favorite movie. Someone cast her in the threequel.