Jean Shepherd, from Indiana originally, is a radio monologist whose show has been broadcast "live" every night for years by a strong AM station in New York City. Recently other stations around the country have started running his tapes, and he has been narrating a series, "Jean Shepherd's America," on public television. His collections of reminiscences and observations in book form, of which this is the third, have sold out big printings, though their titles never appeared on the New York Times best-seller list. A part of their sizable readership (Shepherd's books are probably not only bought, but read) is very likely drawn from the same audience that is devoted to Playboy - it was in Playboy that many of Shepherd's philosophical anecdotes first appeared in print, and he has the unique distinction of winning that magazine's "Humor Award" four times. Thus Shepherd is something of a success in the mass media. . .