One way that I shut down the crazy chatter box in my head is to set it straight with a commitment statement.
It may strike you that I should indeed be committed (to the looney bin) upon admitting I have crazy talk in my head, but I don't think I'm the only one :) I long ago resigned myself to the eruption of irrational self-talk. I no longer resign myself to its longevity though.
Now, when I feel the anger, anxiety, worry or fear, I just make one statement in my mind that is pretty successful at shutting it down. All I say is "I'm not committed to that."
That is an absolutely true statement that brings an immediate shift. I am not committed to worry. I am not committed to chaos or disorder. I am not committed to petty anger.
If I walk around with self-talk that supports those notions, I am indeed crazy. If I allow groundless emotions space to live and breath in my thoughts for any length of time, my quality of life is seriously affected.
If the idea of "I'm not committed to that" doesn't shut down the chatter box, I often continue on with a statement of what is that I am committed to. For example, when I feel worry or fear show up, I often counteract that with "I'm not committed to that, I'm committed to ease and joy."
I'm committed to strength, power, joy, growth, ease, prosperity, love, respect, dignity, creativity, connection, ..... that's the stuff that I allow to occupy my mind.