Humor is the overt expression of feelings without personal discomfort... and without unpleasant effect on others. Humor allows one to bear, and yet focus on, what is too terrible to be borne. This stands in contrast to wit, which always involves distraction or displacement away from the affective issue.
Hmmm. It's never pleasant to think that such a big part of one's personality is considered a 'defense mechanism' (albeit a more developed defense than: "I know you are, but what am I?" -- which may be what they mean by 'projection').
But the psychiatrists have a point; there clearly are times when a joke is pathological. Shouldn't psychiatrists be more precise, however, and call this defense 'gallows humor' ?
Sure, Tom Green's bout with testicular cancer, immortalized in the funny show, "Tom Green's Testicular Cancer Special", can be construed as a humor defense. But does that mean that everything else that's funny is wit? Steven Wright, yes. Gallagher, no.
If Gallagher isn't witty, and he's not, then his watermelon-smashing routine must be shielding us from something too terrible to be considered. The psychiatrists may be on to something: I recently heard of a man who only laughed when planning morbid pranks. One such plan was to put clothes on a watermelon and throw it off a building, confusing and horrifying the people below. This, indeed, would be too disturbing to contemplate without Gallagher having paved the way.
On a more serious note: if humor is a defense, why isn't it invoked immediately after a trauma? Why do we have to wait a few days, weeks, whatever, before we can "look back and laugh at it"... it seems the best time for the defense would be when the stimulus is most painful.