I'm so pissed off at myself.
What are you pissed off about?
I knew exactly what I wanted to say, but I just didn't know how to say it.
Sometimes we can't think straight when we are upset. It's okay to be mad sometimes but you have to try to calm down.
But I don't want to calm down...
I understand that you're upset, but remaining angry isn't going to help anything. Once you cool off a little bit you'll be able to collect your thoughts and figure out what you want to say.