Listening to a Something Understood episode on Schadenfreude, I was struck by this quote in Hobbes' Leviathan. He argues that those with the least self-confidence are most likely to laugh at the defects of others. I think I have been guilty of this flaw, and it's been especially revealing since I suffered a bit of a setback at work.
Sudden glory is the passion which maketh those grimaces called laughter; and is caused either by some sudden act of their own, that pleaseth them; or by the apprehension of some deformed thing in another, by comparison whereof they suddenly applaud themselves. And it is incident most to them, that are conscious of the fewest abilities in themselves; who are forced to keep themselves in their own favour, by observing the imperfections of other men. And therefore much laughter at the defects of others is a sign of pusillanimity. For of great minds, one of the proper works is, to help and free others from scorn; and compare themselves only with the most able.