Related Clues:

• ''Forget it!''
• ''Not at all,'' vernacularly
• Dismissive exclamation
• Strong denial
• At all, slangily
• ''When donkeys fly!''
• See 19 Across
• 'Impossible!'
• ''Don't hold your breath!''
• On the 31st of February
• ''Not a chance!''
• Not at all, in dialect
• 'No way, no how!'
• 'Not on your life!'
• 'When hell freezes over'