3. Tiaras are exclusively worn by married women.

The rationale is that wearing a tiara denotes “adulthood.”
Exception: None
Even as a member of the Royal Family, diamond tiaras are not something you can wear carelessly. The jewelry collection of the Royal Family is valued at millions of dollars, and some of the most costly items include diamond tiaras.

Only married women wear tiaras. ©Chris Jackson/Getty Images
Since they wouldn’t exactly make a practical accessory for a trip to McDonald’s, tiaras should only be worn at night and at the most formal gatherings. These million-dollar trinkets are only allowed on married ladies, which is why Kate Middleton was never seen without one until she wed Prince William.