Related Clues:

• Being rude on the phone, sending e-mail flames, etc.
• This number and those numbers, they're all inadvisable
• They're frowned upon
• Cake and ice cream, to dieters
• They're not allowed
• Running with scissors and others
• Pitchers' hitless games, in baseball slang
• They shouldn't be done
• Discouraged behaviors
• Plagiarism and such
• Thou-shalt-nots
• Verboten things
• Spooky quality
• Things that shouldn't be done
• They're unacceptable