M.K.
My three year old with PDD-NOS was fixated on Shut Up. Everytime she would say it I would tell her "No, we say sush." and make her say sush. When she would say sush I would tell her good job and leave it alone until she would say shut up again. I'm not saying it is an instant fix. However, she no longer says that word on a regular basis. Hopes this help some.