From the moment he left Eton, Nicky Haslam was the life of the party, a dazzling young charmer who enchanted the good and the great—Joan Crawford, the Rolling Stones, Cecil Beaton, Bill Blass, etc., etc.—ushering in Swinging 60s London, introducing Andy Warhol to New York society, and seducing Hollywood stars of both sexes. As Haslam publishes a memoir, at 68, and settles into his face-lift, our author hangs out with the interior designer and man-about-town to discover what lies beneath the…