Take it from a guy who has an Ex Girlfriend who has been torturing me since the day we broke up July 4th of last year. Yes, it was independence day now. I remember it.
She does these things....because she knows she can make you angry. She is your ex after all, she knows how to push all the right buttons. Like Monkeystyle said, let it go. Don't allow her inside your mind any longer. The anger is not worth your future. And its a bright one Stinger, believe me.
You need to release some tension? Meditation. I know, its cliche and a horribly crappy answer, but it really works. Martial Arts and Meditation. Calm the spirit and calm the mind and body too. Realize that she is simply a bitter, hopeless wretched whore, who will never be happy because every waking action she does is simply to try and piss you off. She has a horrible life, and thus tries to ignore her own insecurities by trying to inflict pain and misery on you.
Don't let it happen.
I myself....every night for the past 8 months...have had nightmares about Cassie. I can't get her out of my head, I always imagine her and how I may never find someone else. But she doesn't make me angry anymore. She tries to call me, I act nonchalant. Because I know she's pathetic in her attempts to make me care again. Even if I can't get her out of my dreams, I can prevent myself from being angry and hurting others. You too....can do this.