Blithe, wanton and insouciant, Sylvia Wright talks back. At the sexual anthropologists who say America's a woman's world. (How can it be, she retaliates, with fluorescent lights in it?) At those fatuous articles by the once-obese- now slender. Her comeback --How I Lost A Pound and A Half In Six Weeks. At magazine recipes which presume a fully stocked larder every day of the week and a refrigerator bare of left-overs. Miss Wright wryly admits that she is on one non-stop recipe with a left-over base from one summer's end to the next. Her salty and astringent observations on Life's little lunacies, and her reactions to them, will encroach on the circle of readers who second the motions of Dorothy Parker and Phyllis McGinley-- although her commentaries are not as barbed as the former's nor as air-borne as the latter's.