Forbidden double negative?

• Taboo that may be worthy of a time-out
• Unwise act
• It's verboten
• Off-limits activity
• Frowned-upon activity: Hyph
• "___, Nanette"
• Something you shouldn't do: Hyph
• Nail-biting, e.g
• ''___ Nanette''

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