By Hunter Oatman-Stanford — You've heard it before, and no doubt you'll hear it again: Cosby sweaters just won't go away. The ubiquitous gaudy knits, named after those worn by comedian Bill Cosby on "The Cosby Show," are coveted by everyone from irony-laden thrifters to fashion's top designers. Not unlike the ugly Christmas sweater trend, Cosby's flamboyant knitwear remains a cultural touchstone. But beyond our nostalgia for the ostentatious ’80s, the reasons why the world went Cosby-sweater crazy—even as their...