Related Clues:

• Yup's alternative
• 'That's a lie!'
• Informal denial
• Slangy refusal
• Slangy turndown
• 'Forget it!'
• 'Don't think so'
• 'No way!'
• 'Nah!'
• Slangy denial
• 'Uh-uh'
• 'Don't sweat it'
• 'Nope'
• 'No sirree'
• Rebuttal to 24-Across