He is the primary reason why men largely stopped wearing hats in the 1960s. JFK mostly avoided hats, which were commonly worn by men for many decades.
JFK was the last president to be inaugurated in formal wear--top hat and tails. But, despite the frigid weather, he removed the top hat and overcoat for his inaugural speech. Very little footage remains of JFK in a top hat (as he drove to the inauguration with Eisenhower).
