An interesting question.

For me, occurrences like this are invariably a problem of mindfulness. Thoughts are tricky things because to the individual they are a concrete experience. I start thinking about a foreign situation, which at some point leads to thoughts of what might go wrong, which then ends up triggering actual feelings of anxiety. Suddenly, if I let things get out of hand, the simple act of considering a new situation has essentially activated a fight or flight response.

After a while, like any well ingrained habit, this whole process is perceived as almost compulsory. And to some degree it is; one cannot stop or suppress thoughts through sheer power will. Nor should they try. It will lead to nothing but more suffering. They are the conscious brain's unavoidable musings on the stimuli it receives from the world.

What you can do is choose which thoughts to entertain and how to respond to them. It's kind of like when you debate things in your head and are testing out answers on yourself. You're going through the arguments and in response to one you may inadvertently think something prejudice, racist, sexist, or something otherwise socially unacceptable. Now that's not a bad thing in and of itself. What's important at that point is that one assesses it, realises the thought is not socially acceptable and why, and dismisses it as invalid. What would be bad is if one accepts that thought as okay simply because it’s the one that cropped up. And then follows through on it some capacity.

The same process is applicable to emotionally charged thoughts which arise when in situations like your post. A thought crops up in response to a stimuli. It is a thought which has connotations of anxiety, anger, sadness, etc. But just like the prejudiced thoughts, it can be assessed rationally. What is this thought? What is it a response to? Why? What influenced it? How is it making me feel? Is it rational? Why/why not?

After this assessment one can ask themselves this question: Is it an acceptable thought/the thought I wish to have?

If the response is ‘yes’ then follow the thought some more. But If the answer is 'no' then you let go of the thought and no longer consider it. It is a passing cloud. This whole process should ideally be as non-judgmental as possible, i.e. not judging the thought as positive or negative. It is a natural response to stimuli. This stops the process before it gets to a point where it makes you feel anxious. One does not have to follow it through to its conclusion.

Of course, this is harder than it appears in writing. Thoughts can return or become invasive etc. This technique is generally practiced in session dedicated to mindfulness. But for me, this has been the key to overcoming my anxiety. And I was guy who would have 30 minute debates with himself about whether to accept an invitation to the pub.

I’d like to write more but I’m at work right now but I’ll reply later if this helps at all.