In “The Devil Wears Prada,” Meryl Streep, as the invincible New York fashion editor Miranda Priestly, never raises her voice. To snarl or shout would imply that some resistance to her authority exists, and none does. In the most matter-of-fact way, Miranda has reduced her staff to a state of hyperventilating fear. At the offices of the thick fashion monthly Runway, the perpendicular girls in John Galliano and heels race through the corridors like cranes on point; one girl, running across the street on a meaningless errand, gets knocked down by a car. Despite these desperate efforts, Miranda insists that she’s a victim of universal lethargy. Day after day, she’s perplexed by the ineptitude of the staff. Lowering her chin slightly, Streep stares at the young women who work for her until their knees knock; she speaks in petulant fragments, leaving out the information that they need, then dismisses the baffled employees with a flutter of her wrists. Streep, a brilliant comedienne, pushes the terror tactics into satire, but the comedy moves in a shrewd direction: Streep’s every gesture says that fashion is a multibillion-dollar business in which civility (except when directed at the famous) has become a disposable luxury. Miranda is a calculating monster—she has excised any remaining trace of softness from her temperament—but she understands her role in fashion so acutely that you can’t make fun of her. In all, this has to be the most devastating boss-lady performance in the history of cinema.