Straight: Alice, a beautiful blond heiress who happens to be a cheerleader and the most popular girl in school, goes out of her way to be a bitch to Becky and Claire, our heroes.
Alternately, she's only mean to Becky and Claire because of a legitimate grievance she has against them, possibly of their own making. Once that's dealt with, she eases up.
Alice has the looks, the wealth, and the personality, but zero charisma, so everyone just ignores her.
Double Subverted: But she was only saying that to get sympathy from Becky and Claire.
Parodied: Alice is a total ditz and an obvious asshole, but when she passes by, everyone turns into mindless masochistic robots.
Deconstructed:
Alice realizes that she's an awful person, and feels guilty.
Everyone realizes what a bitch she is and the mere appearance of her turns off everyone
What she thought of as "popularity" was actually the result of people living in fear of her.
Zig Zagged: Alice just wants friends...but that was an act...or at least that's what she claims, not wanting Becky and Claire to know that, just like anyone else, she has a weakness...
Averted: Alice is of normal temperament.
Enforced:
"It's a series about high school. There has to be one girl with a bug up her ass."
Played For Drama: Alice's cruelty causes severe and permanent psychological damage to Becky, sending Claire on a Roaring Rampage of Revenge. This makes Claire Not so Different from Alice.