In 1922, if your bathing suit was too short, it warranted police action.
We stumbled across the photo below on Retronaut. It shows a policeman using a measuring tape to verify the distance between a young woman's knee and bathing suit bottom at the Tidal Basin in Washington, D.C.
According to the Library of Congress, "Col. Sherrell, Supt. of Public Buildings and Grounds ... issued an order that bathing suits at the Wash[ington] bathing beach must not be over six inches above the knee." We're pretty positive that law would NOT fly today.
LOOK: Bathing Suit Law Being Enforced In 1922