Whoever thought that a movie based on a parenting book would become such a cult hit? Tina Fey, that's who. She adapted Queen Bees and Wannabes, peppered the script with zany Saturday Night Live humor and threw in a dash of her signature non-sequitur comic touch. It was the perfect recipe for a hit. Mean Girls descended on cinemas on April 30, 2004. Fifteen years later, it's still a touchstone of popular culture. There's even a Mean Girls Day—it's October 3rd.