It sounds like the premise of an especially horrific nightmare: You're on stage in front of at least 100 strangers. One of them yells out the phrase "Silly String in the Desert." And then the crowd, who all paid $15 to be entertained for the evening, expects you to use that phrase as the title of the completely improvised 30 minute musical you're about to perform for them. Now...go! Be funny! And hope that if you say something, well, not so funny, another performer is there to pick up the slac