Related Clues:

• "Dream on!"
• Slangy turndown, and a hint to how 17-, 22-, 32-, 47- and 51-Across are formed
• 'Yep' opposite
• 'Ain't happening'
• Yup's antonym
• Opposite of "yup"
• 'Not gonna happen'
• Opposite of 49-Across
• Opposite of "yep"
• "Sorry, can't"
• 'Uh-unh'
• "Forget about it"
• "Nothing doing"
• Retro refusal
• ''Don't do that!''