B.J. Novak opens his debut feature “Vengeance,” which he wrote, directed and stars in, with a scene of acidic social commentary that lays the tone for the smart satire of contemporary media culture that ensues. In a scene that targets the mating rituals of the urban-dwelling modern American cad, interspersed into the opening credits with an almost jarring violence, Ben (Novak), a writer for The New Yorker, and the unlikely, sometimes unlikeable, hero of “Vengeance,” parries back and forth with his friend John (played by singer John Mayer) about their vapid dating lives. As they debate the meri…