I am not saying all women want to hurt their good friends, however, every woman has that one friend they wish would trip on her stilletos while accepting her "Woman of the Year" speech. Anything you have ever accomplished pales in comparison to her achievements, and as long as you two remain "friends," you will always be playing the supporting female role in the movie of your lives. She would probably cast an older, fatter, version of yourself to play the part of you as well...
If you got a raise at work, her husband bought your company. When you get a new haircut she tells how much better it looks now compared to that train wreck you had going on before. If you lose ten pounds, she is there to deliver you a celebratory dozen cupcakes on her way to the gym.
In most cases, this creature of darkness is one you have known since childhood. You two probably grew up being compared to one another by your parents, teachers, and friends thus setting the bar for the level of competition that will continue until one of you loses and dies first. "I can't believe that bitch got married and had kids first, and now she had the nerve to die before me too? Who does she think she is? Was. My condolences. May God rest her soul."
There is no way to avoid a frenemy unless you can avoid women altogether, and you can't...there's too damn many of us. So just remember, keep your friends close and your frenemies closer. That, and if she tells you how amazing you look at the holiday party, burn that fucking dress. She's lying, and you probably look fat.