Sadistic. That is oddly enough a fairly good way of putting it. I think the idea of a tortured artist comes from the deep, complex, emotional meaning often attributed to pieces of art. A lot of emotion gets put into art both fine art and preforming arts. In order to create such an emotional piece of work one must be overflowing with passion and feeling, shouldn't they? I may just be grasping in the dark here.
For me, I put a lot of myself into my art. Good and bad aspects and everything in between. I do have many pictures that are fueled by intense negative emotions. But first of all, I am not the only person with these emotions, everyone has them including people who aren't artists of any sort. And second, these emotions give my inspiration, but they do not get work done. When I'm mentally I can't finish a damn picture.
On a slightly related note. There are creative thinkers, and logical thinkers. Neither are better than the other and they have the same feelings, it's just how they respond to these feelings that makes them different. When faced with a challenge a logical thinker will try to figure out the cause, and find a simple solution. A creative thinker wont try to make perfect sense of it, they create something from it. And that's my half intelligent thought of the day.