Possible Clues:

• Flap round and round — that's not acceptable
• Out of bounds, in a way
• Burping in public, e.g.
• Both appreciation and disapprobation are forbidden
• Something not done
• ''The Sweetest ___'' (Sade hit)
• Volunteers rail against something not allowed
• Upset at disapproval when forbidden
• Job, for example, cut after short time - that's unacceptable
• Prohibited by custom