"Kramer's" Racist Tirade - Caught on Tape

Richards, who played the wacky Cosmo Kramer on the hit TV show "Seinfeld," appeared onstage at the Laugh Factory in West Hollywood. It appears two guys, both African-American, were in the cheap seats playfully heckling Richards when suddenly, the comedian lost it. http://www.tmz.com/2006/11/20/kramers-racist-tirade-caught-on-tape/ He later apologized on Letterman and was obviously struck. What is happening here? Is he really shpowing the audience their own underbelly or just freaking out on his own anger, or both, or ...?