by Diana Vreeland. Knopf, $15.95. Diana Vreeland has been editor-in-chief of both Vogue and Harper’s Bazaar and, more recently, the curator responsible for exciting fashion-as-art exhibits at the Metropolitan Museum. She has known interesting and important people in the world of art and fashion since the 1920s. She unquestionably has a brain, and why she has chosen in this memoir to pretend that her head contains nothing but sequins and caviar is a real puzzle. Can all this resolute frivolity result from the influence of George Plimpton and Christopher Hemphill, who are inexplicably listed as editors of the book?