Have you heard the one about the wisecracking political prankster who switched to stand-up comedy? No one could tell the difference. Erstwhile Yippie Abbie Hoffman, fresh from a reunion of demonstrators from the 1968 Democratic convention in Chicago, made his New York comedy debut Monday night at an Upper West Side club. Hoffman, whose humor and courtroom antics got national attention during the Chicago 7 trial, spent more than an hour needling "Actor in Chief" Ronald Reagan and the Republicans, and reminiscing. Predictably, vice-presidential candidate Dan Quayle came in for a few jabs: "looks like a hawk, runs like a chicken."