Possible Clues:

• Emphatic denial
• 'Yes, you are!' retort
• Retort to "You are too!"
• Indignant denial
• Answer to an accusation, maybe
• Retort to 'You are a liar!'
• "--- a crook": Nixon
• Lead-in for a crook?
• 'You are so!' preceder
• Response to an accusation