Essentially, to "catastrophize" is to overreact in a negative way to a setback, such as the one who is stood up for a date and becomes upset that he or she will never find love. Broadly, catastrophization is a habit of mind that's commonly identified in the anxious and depressed. I don't know enough to speculate about what causes the formation of such a habit, but I can admit to recognizing it in myself. I have often characterized my depression as "an inability to control negative thoughts," and by these negative thoughts I essentially mean overwhelming catastrophization. When I'm depressed, even the smallest and most innocous event or impression can become symbolic of my total failure as a human being.
Recognizing the process as a habit, as something that can be lost or changed or replaced like any other habit, is itself very valuable to me. Even the simple fact that there exists a word to describe the phenomenon brings me considerable comfort--in the first place, it shows that I'm not alone in experiencing it, and in the second, well...everyone knows that to name a thing is to have power over it. The next time I begin to "catastrophize," the word itself will occur to me, and in matching the sign to the signified I will be reminded that the catastrophe I perceive is in my head and not in the world. Maybe, in time, I'll even be able to laugh about it, to find some humor in the extent to which I can blow things out of proportion, but of course there's a fine line to be walked here. I can already hear myself thinking: "I'm catastrophizing again. It's so like me to do that. No wonder I'm a such a TOTALLY WORTHLESS LOSER."
As in learning to meditate, the trick to changing habits of mind like catastrophization is probably to avoid trying too hard. Instead of recognizing catastrophic thoughts and working really hard to stop, it's probably better to just recognize those thoughts, release them, and then casually replace them with something else. Those three Rs could become a mantra: Recognize your negative habits, Release them in the moment, and Replace them with something more constructive. Perhaps there's even a fourth R: Repeat the process until they change.