It's always a good time to bash Simon Heffer. Like Heffer, I do think that the hat should make a comeback. However it is simply untrue to say that President Kennedy was responsible for the decline of hat wearing. Usually this myth states that the decline in hat wearing began when he declined to wear the traditional top hat during in inauguration, and being such a style icon he immediately made head wear obsolete.
The one slight flaw in the theory is that during his inauguration he had a great big hat shaped item on his soon to be splattered bonce.