The humanization of Mitt Romney got a hand from some professional comedy writers last night on David Letterman’s Late Show, as the GOP candidate stiffly read from a script. During the brief “Top Ten Things Mitt Romney Would Like to Say to the American People” segment, his second of the year, the former governor had on a blazer, but no tie, like the cool dads do. He also made a football joke and used slang. “What’s up, gangstas? It’s the M-I-Double Tizzle,” he deadpanned, live from the year 2000. But amid the self-deprecation was one barb — “Newt Gingrich? Really?” — made sharper by Romney’s well-timed, perhaps inevitable, return to front-runner status.