I think the worst type of person to find yourself in a toxic friendship with is the girl/guy who tells you that you matter with words, but hasn't backed up the lip service with their behavior in quite a long time. They used to walk the walk once upon a time, so you forgive and forget on the first instance they fuck you over, but then it happens again... and with more frequency.
We all have to deal with (or hopefully had to deal with - past tense!) friendships that, for whatever reason, are no longer healthy for us to be a part of. Usually these relationships run their course and die of neglect, but sometimes we have to purposely radiate them from our world like the cancers that they are. I find myself in that situation now.
The first time Friend X let me down I let bygones be bygones because the separation was painful and we had a solid past friendship that seemed worthy of salvaging. A few instances later and I feel... nothing. Literally nothing. Just total, 100%, unadulterated apathy. When the apathy stage has been reached, only the truly foolish continue on and play the lip service game. I am many things... loyal, honest, sensitive, sometimes bitchy and sometimes high maintenance... but I'm nobody's fool.
Be good to your friends, ladies and gents. Like all other relationships, you lose what you abuse.