Possible Clues:

• "The Sweetest ___" (Sade hit)
• It's not done
• Maligning 2-Down, in some places
• Prohibited, sacred
• Time to show disapproval, to introduce a ban
• Forbidden for social reasons
• Many a fetish
• Out of practice Customs won't allow it
• In Chinese culture, gifting someone a clock is one
• After end of concert a disapproving word is not allowed