Ending a relationship stinks, and it may be even worse when you have to end a relationship with a friend. When you're young and just learning how to support your friends and what to expect from platonic relationships, it's easy to overlook potential problems, like narcissism, liars, bad secret keepers and Debbie Downers. As we age, however, knowing how to be a good friend should be fairly obvious. And when a friend consistently shows that she isn't willing or doesn't know how to do the things that good friends do, then it's time to make a change in your relationship. Here are a few ways to know if your friend is toxic. Friends should be happy for your accomplishments, and if you don't find that your buddy is happy for you - or worse, tries to one-up you every chance she gets - then that can be a relationship killer. So can the friend who never has anything positive to say. You might ask this Debbie Downer how she's doing and get a laundry list of everything wrong in her life in response.