All too often. Some of the angriest, darkest, nastiest people I've ever met were stand-ups -- myself included -- which is why I got out of it and into (hold your laughter!) lefty politics. (Though after my little triumph the other night, the wife wants me to go back in.)
Sometimes the anger can be righteous -- look at Bill Hicks, who also showed a lot of tenderness and humanity in his act. Richard Pryor at his best infused his work with pathos and a touch of humility. There are others. But in the main, at least in my travels, stand-ups are just fucking pissed off.
DP