Game in which a pitcher doesn't allow any knocks

• Double-dipping, to some
• It's to be avoided
• Off-limits word
• Eating peas with a knife, e.g
• Ringo Starr's "_____ Song"
• Thing not to do
• Prohibited activity
• Something best avoided
• Smacking one's lips while eating, e.g

Wiktionary Word definitions in Wiktionary
n. (alternative spelling of no-no English)