Former Friend of Alpha Bitch

Most stories that are in a school setting feature a mean, but insanely popular girl and a likeable, but considerably less popular girl who will invariably be at odds with each other. In the worst case scenario, each will routinely be at the other's throat. (That may form a great deal of the story's plotline.) Even in the best case, these characters will rarely be able to share a civil conversation. Either way, it's very unlikely that these two characters will ever be friends.

Except that, in some stories, they were friends at one point, but some kind of rift came between them and split them apart. Common causes of the rift are a romantic entanglement in which one ended up with the other's boyfriend or the simple fact that the Alpha Bitch became popular and the Cool Loser didn't. In stories of this type, don't be surprised if the Alpha Bitch and the Cool Loser eventually start on the path to being friends again. At the very least, the Cool Loser may express the sentiment that popularity has changed her friend and that she wishes things could be the way they were before.

Anime and Manga

 * in the anime of Oniisama e.... More exactly:, and now in highschool they hate each other.

Film

 * Stacey and Anna in the 2003 version of Freaky Friday. Notably, Tess thinks this can be solved with a heartfelt speech, which blows up in her/Anna's face almost immediately.
 * Janis to Regina in Mean Girls. In an interesting variation of the trope, Janis proves to be almost as bad as Regina.
 * Heathers had this, only with the old friend being a minor character. Turns out Heather D., who is becoming the new head of the school's food chain, was once best friends with the unpopular, unattractive, and obese Martha "Dumptruck" Dunnstock. Heather D. is so ashamed of this that when she finds out J.D. has photographs of the two of them playing together, she pays him to get rid of them.
 * Averted with Veronica and her best friend Betty. They are still friends but don't get to hang out as often due to Veronica being seized by the popular crowd. They reunite by the end when Veronica severs ties with the Heathers (Whom she didn't really like to begin with).
 * The title character from Jennifer's Body is the Alpha Bitch; the narrator is her best friend and a Hollywood Nerd . The entire film is about the main character escaping from this relationship.
 * The original version of 101Dalmatians invokes this, although the characters have long since finished school: "Oh, must be Cruella, your dearly devoted old schoolmate."
 * Amy to Dylan in Geek Charming...though she still considers Dylan a friend regardless and wishes for her to get over her Alpha Bitch-iness so they can hang out together again, which happens in the end.
 * Inverted in 13 Going On 30 where the Alpha Bitch is Jenna's best friend when she's 30 but they didn't get along in school.

Literature

 * Chantal Simmons in The Geek Girl's Guide to Cheerleading. She used to be friends with the heroine when they attended the same dance school, but Chantal became a cheerleader and the heroine became a nerd. This marked the end of their friendship.
 * Samantha Deveraux in Marlene Perez's Dead Is series. In the first book, Dead Is the New Black, the heroine mentions that she and Samantha were friends until they had a falling out. By the beginning of the second book, Dead Is a State of Mind, they're working on becoming friends again. It helps that Samantha's bitchiness is mostly an act.
 * Lasaraleen from The Horse and His Boy. Although she and Aravis weren't the chummiest of friends, they did have a history together.
 * Not to mention, Lasaraleen is more of a Brainless Beauty than a true Alpha Bitch.
 * In Amelia, a variation happens where Amelia and Lucinda are best friends at the start but once Amelia's family loses their money, Lucinda acts more like an Alpha Bitch and looks down on Amelia for being poor.

Live Action TV

 * Kate and the titular heroine of Lizzie McGuire. Something of the sort happened when Kate got dethroned by Claire.
 * In Buffy the Vampire Slayer, it was established one time that Cordelia, Xander and Willow all used to hang out together when they were preteens. Cordelia becomes more friendly with the Scoobies once she starts dating Xander, but then goes through another phase of being their "ex-friend" after he cheats on her with Willow. They apparently make up eventually, at least to the extent that Cordelia calls Willow in an episode of Angel', though calling them outright friends might be pushing it since Cordelia only found out Willow was a lesbian after she had been out of the closet for a whole year.

Webcomics

 * The now-ended webcomic As If had Hunter and Sandy, who used to be BFFs in junior high. (Hunter even says Sandy used to throw amazing Risk parties). But as time went on, Sandy got into makeup and boys, and Hunter...well, let's just say she didn't.
 * Penny and Aggie: Apparently Helen used to be friends with Penny and is still bitter.
 * Sayuri Morita of Red String used to be friends with Miharu and Reika in middle school, but after only Miharu and Reika were chosen to appear on a sidewalk TV show, she became obsessed with being popular and pretty much declared them her enemies. Flash-forward to high school where she's given herself a new image, gained a clique, and keeps making Miharu, Reika, and Fuuko's lives miserable.

Web Original

 * In Sailor Nothing, Aki has a falling-out with Ami after the former's yamiko ruins her reputation. It's actually the best thing that could have happened to Aki, who finally sees how shallow her life had been.

Western Animation

 * Sharon and Alpha Bitch Nina from Braceface. They were friends as little girls, but one day someone destroyed all of Nina's dolls and she blamed Sharon.
 * On The Spectacular Spider-Man, Peter and Flash used to be best friends as children, and in fact still live right around the corner from each other. Flash's mother doesn't seem to realize they had a falling out a decade ago, as she wound up sending Peter an invitation to Flash's birthday party.