The most underestimated quality of successful stand-up comedians is how hard-working they are, which became clear as this joke evolved over two months. Stand-up is the rare form that usually requires test driving in public. Myq Kaplan, a respected regular at the Comedy Cellar in Greenwich Village, has since tried variations of his chivalry joke at about 80 performances. Almost every time, he tapes it, studies the results and jots down new ideas. That’s the job, he said, one he can’t imagine ever not doing.