Related Clues:

• Unmentionable
• "I forbid you!"
• 'Cease and desist'
• Bad thing to do
• Discouraging word
• Slurping at the dinner table, e.g.
• 'Stop that!'
• Echoing taboo
• Forbidden act
• Not allowed
• Using metallic dishes in a microwave, e.g.
• 'No!'
• Something not to talk about
• Cell phone ring in a theater, e.g.
• It's frowned upon