Thought stopping is the habit of watching one's own thoughts, and deciding when you have had enough of a certain thought that is bringing you down. Many people do not realize that unwanted thoughts can be stopped just by refusing to pay attention to them. You can also decide not to increase the power of certain thoughts by not verbalizing them.
You don't have to say or think ANYTHING you don't want to say or think. Even if an unwelcome thought comes back, you can stop it over again until it loses its potency. We have much more power than we realize when it comes to controlling the chattering of our minds. The idea of thought stopping is a cognitive behavioral technique, well documented to be applicable to most situations. I personally think of it as reclaiming one's own mind.