Related Clues:

• 'Why ___?'
• 'Clueless' interjection
• "Ain't happenin'"
• Word with so or interested
• "Impossible!"
• Catchphrase for 26-Down
• ''Forget it!''
• Negative function word
• National Do __ Call Registry
• Yup's opposite
• ''No way''
• With 40-Across, later
• Naysayer's word
• 'Nuh-uh'
• 'Shyeah . . .'