Barnardine is a drunken prisoner scheduled to be executed the same day as Claudio the fornicator. In order to save Claudio's life, the Duke hatches a plan to substitute Barnardine's head for Claudio's, so that Angelo will be tricked into thinking Claudio has been killed.
Barnardine, however, refuses to cooperate. When he's told he's headed for the chopping block, Barnardine insists that he says he's way too hungover to die and heads back to his cell to sleep it off.
(Hmm. We wonder if this where Herman Melville got the idea for his famous character, Bartleby the Scrivener, who always says "I prefer not to" whenever his boss asks him to do something.)
Barnardine's flat-out refusal to be executed is both astonishing and amusing for its flagrant disregard of the (corrupt) authorities in Vienna. We think the famous nineteenth-century literary critic William Hazlitt said it best when he wrote that "Barnardine is a fine antithesis to the morality and the hypocrisy of the other characters in the play."