Listening to celebrity rants has turned out to be one of the great pleasures of the Internet. Mel Gibson threatening the mother of his child, Christian Bale taking apart a director of photography on the set of a film, Alec Baldwin calling his daughter a “pig” on her voicemail — these are the audio clips played again and again, months and even years after they were recorded. But Americans have enjoyed listening to people go off the deep end far longer than the Internet has been around. And the windbags don’t have to be celebrities, either. Case in point: the subjects of the documentary “Shut Up Little Man! An Audio Misadventure.”