Try to pick a word to describe Jean Shepherd and he'll no doubt argue that you're wrong. Actor, writer, humorist, comic, story teller, satirist, philosopher - all these terms come to mind during an evening with the performer who gave a one-man show before 1,000 people at the Clinton Historical Museum Saturday, July 20. One image Shepherd is trying to shake is that he is trying to invoke nostalgia. That label is applied to him only by older people, he said. Young people identify his themes with their own time. "I'm not about the old days," Shepherd said Saturday, as he relaxed before his show with several museum trustees in the Clinton House. "My good work is not nostalgic. Good work surpasses time. Every one of my stories is anti-nostalgic. I think that's one of the great American sicknesses, by the way. Today is the only day we've got. If you believe in the old days, you live in the past."