An All-Star Toast to the Improv (1988)

To celebrate the "birthday" of the famous Improv comedy club, 6 famous comedians get up on stage and do their thing. However, to make things interesting, while each one does his particular routine, the other 5 comics sit at the back of the stage and heckle the performer. This video is especially notable for Martin Mull issuing a zinger at Robin Williams that shuts-up the otherwise motor-mouthed comic for at least 5 seconds.