Mean girls aren't exclusive to live-action movies written by Tina Fey - they appear in anime too!
Anime mean girls are students who delight in harassing their female classmates. While each one has her own reason for being a bully, most tend to act out of jealousy. They might be jealous of a girls' grades and appearance, which is how Rin Sasaki feels about Urara Shiraishi in Yamada-kun & The Seven Witches. Or, like Motoko Minagawa from Fruits Basket, she might want her target to step away from the man she's into. Others aren't acting out of jealousy, but rather, personal gain - Aya Kuroda from Hell Girl just wants money. Some of these girls go on to mend their ways and befriend their targets, while others never repent or suffer the consequences - do not watch Narutaru unless you want to see a particularly brutal example of this.
Let's take some time to appreciate - or hate on - the anime mean girls who pop up in the shows we love.