John McEnroe was the tennis player to beat in the '80s (154 tournament titles). Now he has conquered the bestseller charts, landing in the #2 nonfiction slot with his autobiography, You Cannot Be Serious. So far, the Putnam book has 142,000 copies in print. McEnroe began his publicity blitz in New York City on June 11, a day after returning from covering the French Open for NBC. In addition to the national shows (interviews on Imus, Today, Charlie Rose and Late Night with David Letterman) he has also done a full complement of sport media. Each of his signings have drawn crowds of several hundred fans. After his U.S. tour, the author is headed to London to promote the U.K. edition and to cover Wimbledon for NBC (he won that title three times).