Nate Bargatze is not a dumb guy. He just plays one on TV . And, of course, onstage in his act, in which the 47-year-old comedian from Old Hickory, Tennessee, adopts the persona of a middle-aged everyschlub befuddled by modern life and expectations of basic competence. You know this veteran comic is not a dim bulb — nobody doggedly builds a stand-up career that takes them from clubs to theaters to selling out arena tours from a foundation of genuine stupidity. But you do get the sense that guy