The group of actresses dished to Entertainment Weekly about what it was like on set, and whether they had any idea that the movie would take on such a life of its own.
McAdams recalled a time recently when she visited Europe and was caught off guard by a die-hard fan of her infamous character, Regina George.
"I was staying at a bed-and-breakfast recently in the-middle-of-nowhere Ireland. And one of the owners' granddaughters came up to me, and she gave me a piece of pink paper and she goes, 'Can you write down just a few of your favorite Mean Girls quotes?' It was so sweet," she explained.