Possible Clues:

• "You ___ kidding!"
• 'You ___ kidding!'
• Failed to be
• Didn't exist
• Missy Higgins "They ___ There"
• "As if that — enough ..."
• "If it __ for ..."
• Cole Porter's "___ We Fools"
• "As if that ___ enough . . ."
• Common contraction