Get in, bitches: We're going singing. We couldn't believe it when we learned that the Mean Girls musical was not only happening, but opening in Washington, D.C. on October 31 , just in time to bust out our truly scary Cady-inspired Halloween costumes (the scarier, the better). Now we have even more of a reason to celebrate, because the show has finally been cast! If you thought that the Plastics holiday dance was great, wait until you see who's in the show.