Maybe I should add that I think JFK hastened the process, but it likely would have happened anyway. It was connected to the Countercultural Revolution, which more or less coincided with Kennedy.
It wasn’t just hats. It was also suits, neckties, sports jackets, dinner jackets, and all the rest of what used to be formal wear.
The first time I visited Europe, in the 50s, EVERYONE wore suits, ties, and hats. The next time I went, the Alligator shirt had come into fashion (it started in France and rapidly spread), and many men wore those, instead of the suits and ties they had worn earlier.
When I went to prep school, we always wore a tie, although we might loosen it and undo the top button. And gray flannels. And a sport jacket. The only exception was when we wore athletic uniforms.
Not everyone wore hippie gear in the late 60s, but just about everyone shed their suits and ties, unless they absolutely HAD to wear them. And even businesses in NYC did things like allowing informal wear on Fridays.
This was a huge departure from the past, when even the working classes in Europe wore suits and ties. Our ancient gardener in the house we rented in England in 1974-75 wore a three piece wool tweed suit and tie, even while he was weeding the garden or mowing the lawn. He wouldn’t have imagined being seen in public without it.
No longer.
Good.
Clothing ought to be practical, not overly fanciful / idiotic. Function over fashion.
When I was a kid in the fifties, older males “dressed up” when they went outside. Except for when they were working around the house. If you look at photos of crowd scenes from the early twentieth century, you can see that most of the men wore suits and ties and hats. But by the end of the fifties, as I recall with my sometimes faulty memory, it seems only the males sixty and older really dressed up for casual occasions. I never saw old guys in bermuda shorts. Times change.