de rigueur - dur-ree-GUR - strictly required by fashion or by etiquette
Example: "Among teens, showing as much skin or underwear as possible in public is considered de rigueur, as is excessive use of profanity."
As a starter: and as a former teacher in English, I hope to add to reader's vocabulary by presenting a word a day in simple terms that anyone can understand - from current use in publications, radio,TV, etc. Remember: use a new word three times in a day and it's yours forever!