"Don't do that!"

• Talking with one's mouth full, e.g
• Stealing someone's song, e.g
• Prohibited practice
• Bad thing to do
• It's a bad thing
• A doofus might do it
• It's outlawed
• Bringing a bottle of water through security, e.g
• Fattening food, to a dieter

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