When I spoke to Arsenio Hall—whose cool, raucous late-night show, “The Arsenio Hall Show,” I watched at my mother’s hip all through its six-season run, fantasizing about joining him as a guest on its famous couch—he’d just returned to Los Angeles after a gig. About thirty years after the end of “Arsenio” ’s prime, Hall, now energetically seventy, is still a diligent stand-up comic, doing dates alo...