Related Clues:

• "It can't be!"
• 'Zero chance!'
• Defiant response
• "When donkeys fly!"
• 'Not in this lifetime!'
• Not at all, slangily
• "Forget it!" (and a clue to this puzzle's theme)
• "Dream on!"
• "Out of the question"
• 'Ain't happening'
• "No chance!"
• 'That's too hard to believe...'
• "That's too hard to believe..."
• "Not in this lifetime!"
• 'You gotta be kidding me!'