Oh no she didn't! BFF. Best Friend Forever. Sure. That's the way it's supposed to work out.

BEST FRIEND is a lofty and serious role to assume, never mind who makes it to Forever or who makes it to next weekend. As temporary as some BFFs turn out to be, it might make sense to create some new acronyms: BFRN (Best Friend Right Now) or BFUSBY (Best Friend Until She Backstabs You). Yeah, how loosely or earnestly you give a friend the BFF title should stand some credence.

A friend should be a friend because she loves you, not because she needs a Friday-night companion. A BFF doesn't gossip about or lie to you. She doesn't share your secrets on her MySpace page. And a BFF definitely doesn't make out with her best friend's boyfriend.

And yet, girlslife.com has been bombarded with stories of BFFs who turned on their friendships. So we've compiled the worst so-called "forever friends."

THE BF BANDIT 

In different ways, you're close with them both. He's yours. She's yours. But these are not the sorts of things a girl likes to share. The thought of your BFF and BF together? Nauseating.

On girlslife.com "My BFF and I got to lunch early, and we were sitting at our usual table waiting for the other kids when she started telling me all these reasons I should break up with my boyfriend, who is absolutely perfect. I didn't buy it. When he came into the cafeteria and sat down between me and her, she leaned over and French-kissed him right in front of me! Enough said."

Backstabbing meter *****

BFF fix-it The ex-BFF above certainly earned her pink slip. But sometimes the culprit is the guy, not your BFF. If it's deliberate on her part and she's trying to play like it's not important, this BFF is a WFE (Worst Friend Ever).

THE SECRETLY JEALOUS

It could be silly, like your hair is curly and hers is straight--or vice versa. Or it's deeper, like you're good at making new friends while she struggles with social skills. The details don't often matter. She wants what you have, and that can create some ugly behavior.

On girlslife.com "I was by my locker, looking pretty hot (if I do say so myself!) and flirting like mad with Chris, the hottest guy in my grade. To my surprise, he was returning the interest! Just as I was sure he was going to ask me to this party, my now-ex BFF walked up and said, 'Hey, Em, is that toilet paper on your heel?' I shook it off, but then Chris had to go. The next week at that party, we were playing Seven Minutes in Heaven. When it was Chris's turn, the bottle landed on me! While we were in the closet, he turned off the light and said he was glad he was with the hottest girl in school. And he kissed me! So there."

Backstabbing meter ** 1/2

BFF fix-it Jealous friends typically "knock you down" in order to build themselves up. Would your BFF be open to talking about this? If so, you could offer something about her that you find cool or admirable, then make a pact to not be jealous of each other. If she still throws those underhanded envy-darts at you, consider demoting her from BFF status to just a friend.

THE SPLIT PERSONALITY

You think you know her, but then she seems like a whole other person. She's so ... wacky. She doesn't care how her behavior makes you feel. Some days you wonder: Who is this girl?

On girlslife.com "My BFF was a jerk! We had been BFFs since seventh grade. When my boyfriend broke up with me, what did she do? She became best friends with him! At first I was OK with it, but then she hated my new boyfriend. She was going to be late to lunch one day, and she wanted us to wait and eat with her. We didn't want to, so she flipped out! She wrote me nasty notes and cussed me out. Then, out of the blue, she got all nice and said she still wanted to be friends. I broke it off with her because, otherwise, she'd be going back and forth forever."

Backstabbing meter ***

BFF fix-it The BFF above felt left out because her friend got a new guy. Instead of saying, "I need more time with you," she wrote nasty notes. Not so nice. If your friend turns on you, ask if you did something to hurt her. If she still ignores you, leave her to her feelings. She'll likely come to you eventually. And if she doesn't? It's a universal maxim that when negative people are removed from our lives, we're being spared.

THE BLABBERMOUTH

Big secret. Little secret. Any secret is not intended to be told to the world by a BFF. So why does a BFF blab personal info? One word: attention.

On girlslife.com "I used to be best friends with this girl at school. One day, I was telling another friend I'd finally gotten my period. My BFF overheard me and told everyone in school, including the boys! I confronted her and told her she'd hurt me by doing that. She gave me a snooty look and walked away. We haven't spoken since."

Backstabbing meter ****

BFF fix-it Not every BFF is an ace at every aspect of being a friend. You can salvage this friendship by being selective with what you tell her. But if her blabbing is chronic? Tell her where the door is located, and ask her to use it.

THE TWO-FACED

Two-faced girls act all nice to you but then rag on you the minute you turn your back. They tend to trash on others for no apparent reason.

On girlslife.com "My two best friends joined an alliance against me. They started a notebook that they never let me see. One day, I saw it. They had written all about me, bashing my clothes and family. They wrote that I was stupid and how it was sad I liked a guy who would never like me (he's now my BF). I confronted them, and they acted as if they'd done nothing wrong. I'm so over them."

Backstabbing meter *****

BFF fix-it BFFs who cut you down and act like it's no big deal are wretched! With "friends" like that, you may need to wear a helmet and body armor just to get through the day. If your BFFs do this sort of thing, find new friends. Today.

THE MEAN GIRL

The Mean Girl bashes others to make herself feel superior. Being awful to anyone, for any reason, is her way of staying on top. She's a snake, waiting to pounce on nice-girl prey.

On girlslife.com "My ex-BFF and I were having a sleepover, and she told me to bring my swimsuit. As I was changing, she flung the bathroom door open and snapped pics of me nude! On Monday, as I was walking down the hall at school, I heard people snickering and laughing. I went to see what was so funny, and there it was: a huge blown-up poster of my naked body! I turned around, and my 'BFF' was there smirking at me."

Backstabbing meter *****

BFF fix-it Sadly, little more can be done about cold-blooded stunts than to fire her as your BFF. If you're not on One Tree Hill, who treats people this way?

THE SABOTAGER

Things are fine, and then your BFF throws sand in the wheels, so to speak. Whether it's a crush, a school project or a new style, the Sabotager is skilled at ruining all good things.

On girlslife.com "Every time I like a guy, my BFF says she likes him. When I get the nerve to ask him out, she says she's liked him for months! She gets flustered and says she liked him first, even though I liked him first. She says I copy her. Now, I don't tell her who I like because she'll go behind my back and date him."

Backstabbing meter *

BFF fix-it Depending on how your BFF is sabotaging you is the measure of your response. The Sabotager often doesn't realize she wants something until you want it. Your desire for whatever or whomever suddenly ups the value. So talk to her. You could also put things in writing (send her an e-mail about who you're crushing on, for example), to later pull out and show her. If her uncool strategies persist? Talk to her a lot less.

THE VAMPIRE 

She's sooo needy and never makes a decision without consulting you. She calls and texts constantly, and won't do anything without you right by her side.

On girlslife.com "My BFF is clingy. She gets upset if I don't respond right away to her texts or won't follow the routine (like meeting before lunch). I have cousins our age, but they hate my BFF. I can't tell her because she really likes them. Now my cousins never want to hang out because my BFF is always with me. When my BF broke up with me, he mentioned my 'shadow' and how dating me was like dating both of us."

Backstabbing meter *

BFF fix-it Having a friend love you like a puppy isn't the worst thing. But smothering you? Yeah, that's bad. Set clear boundaries. If you can convince her that time apart makes a friendship stronger, you'll be gravy. If she's sucking your energy dry like Dracula, you'll have to decide for yourself if it's worth it.

THE DITCHER

You have plans, and then BAM! She bails on you. You could even be at an event together, and where is she all of a sudden? Gone, that's where.

On girlslife.com "Last summer, my BFF and I decided to go to sleepaway camp. I wanted to drive there together, but she said she'd meet me there. Too bad she never made it. I spent two weeks at camp without her! When I got back home, I asked her what was up. She said her ex-BF had a new girlfriend and she was too upset to go."

Backstabbing meter ** 1/2

BFF fix-it Ditchers are flakes. They don't realize that if you make a plan, you stick to the plan. A fair warning about not putting up with it and you should be good to go. Otherwise, you should make like a banana ... and split!

THE NUT JOB

She's otherwise known as "melodramatic." Often very intense people, Nut Jobs act out their emotions, often in destructive ways. A BFF? If you say so.

On girlslife.com "I left my bike in my BFF's garage. When I went back to get it, it wasn't the same! She had taken a knife and cut my tires and frame. The seat and handlebars were all ripped up! She tried to say someone broke into her garage. Sure. We're no longer friends."

Backstabbing meter *****

BFF fix-it Crazy doesn't get any less crazy with a little talk. Who knows what sets off a Nut Job? Jealousy, insecurity, a lousy lunch? If your BFF does violent things, tell someone. She's not normal. And tell her this: Bye!