I am going to let my dad know that my mom was planning on leaving him when I turn 18.
Would you prefer for you mom and dad to not be together?
I'm not happy with them, I can't take it anymore. I want to hurt them the most.
I don't think you should do that, no matter how you feel about your parents. Saying something like that would only cause more harm. Your mom might have changed her mind, and telling your dad what she said could ruin their marriage.
My mom was a bitch anyway, she had no right to do that.
It is fine that you are not happy with your parents as that is only a natural feeling. However, wanting to hurt them is just not a good way to go about dealing with your pain. You are better off either seeking help, or talking with your parents about how you feel, instead of trying to hurt them.