Quick! Name another movie based on a self-help book?

See what we mean? This kind of source material is super-rare.

Mean Girls, written by Tina Fey, is based on Rosalind Wiseman's Queen Bees & Wannabes, a self-help book for parents who want to help their teenage daughter deal with bullying. We know, we know: it sounds hilarious.

The thing is, one of the script's greatest strengths is how realistic it is. That's kind of the key to satire: It takes reality and blows it up with riotous hyperbole. Every high school in America has its own Regina George, but we're willing to bet very, very few of them got hit by a bus while dressing down a frenemy.

Ms. Norbury Wrote a Movie

Mean Girls' biting, clever, and immensely quotable script is the first feature film from Fey, who you probably know best as 30 Rock's night cheese-loving Liz Lemon and the first female head writer of Saturday Night Live.

Fey read Wiseman's book, and thought there was a movie in it. She brought the idea to her boss at SNL, Lorne Michaels, and, according to Fey, he agreed, on one condition:

"When I first pitched it to Lorne, I was thinking I'd like to write a movie about what they call "relational aggression" among girls. He was like, "Okay, but could they also still have cool cars and cool clothes?" And I was like, "Oh, for sure!" (Source)

Fey's script combines cold, hard facts (from Wiseman's book) with sharp characterizations and humor (from Fey's noggin) to create a high school comedy that's closely observed and richly detailed, but still highly accessible and relatable.

It's a study in pop psychology that could happen anywhere, and Cady essentially functions as Fey's stand-in as she studies the vicious social hierarchy of North Shore, often in disbelief.

Of course, Fey herself is in the movie, too. She plays levelheaded, slightly messy math teacher Ms. Norbury. Ms. Norbury may not quite have her life pulled together, but she's still a font of solid advice for Cady. She's the film's voice of reason, the one who directly calls out North Shore's "girl-on-girl crime" and the preposterousness of their cannibalistic social order.

That's what happens when you write a movie—you can give yourself all the good lines.