The new documentary about comedian Joan Rivers includes a scene where she tells a crude joke about Helen Keller. While appearing at a Wisconsin casino, a man in the audience challenges her about a mean-spirited Helen Keller joke. He yells, "It's not funny if you have a deaf son!" Rivers shouts him down, arguing that comedy is about making us able to face the most painful and awful aspects of life. Joan Rivers: A Piece of Work opens in select cities later this month.