someone who lies alot to you and behind your back. someone who pisses you down on a regular basis. They say they will hang but then they do not and they go hang with a few various other bitchy chick just who she understands you hate. A negative best friend will state they are going to never do something.....and they do it. Bad best friends lie about tips for make us feel sorry for them. They ruin your heart along with your insides until you cant take it any longer. Thats when the prey gets sent to a crazy place or they make sudicide.