Possible Clues:

• Required by etiquette
• Awfully rude urge I suppressed, as required by etiquette
• Called for
• ... in French, having to observe strict etiquette
• It's required by etiquette in France
• It's essential, if you want to speak French
• Required by custom or etiquette
• It's mandatory in France
• For a break, urge ride round University, as required by custom
• Demanded by etiquette, and not only in Paris