Retro: I've only heard of this being applied to the '50s.
Maybe you could use fad as well?
Just some ideas, anyhow.
Regards.

another option!
The Wearing of Hats Fashion History- [ Traduzca esta página ]Plumassiers. The Demise of Hat Wearing. Hat Decline after Wars. Hats for Occasions ... Etiquette and formality have played their part in hat wearing. ...
The Wearing of Hats Fashion History- [ Traduzca esta página ]Fashion History of Hats. Why We Wear Hats. Origin of Milliners. Plumassiers. The Demise of Hat Wearing. Hat Decline after Wars. Hats for Occasions ...
www.fashion-era.com/hats-hair/hats_hair_1_wearing_hats_fash... - 42k - En caché - Páginas similares

A short history of headgear (size 73/4); OLD HAT! WHY THE HEADY ...- [ Traduzca esta página ]In America, the hatless young President John F Kennedy was credited with hastening the demise of hat-wearing among men. And so began the long-term decline ...
findarticles.com/p/articles/mi_qn4158/is_20050504/ai_n14609987 - 30k - En caché - Páginas similares

Hats- [ Traduzca esta página ]The Demise of Hat Wearing Etiquette and formality have played their part in hat wearing. At the turn of the 20th century in 1900, both men and women changed ...
www.freakshop.com/info.php?title=Hats&page=hats - 28k - En caché - Páginas
Google Answers: Hat wearing trends- [ Traduzca esta página ]Another factor in the decline of hat wearing is that hats served to protect hair from dirt, and in that vein, to extend time between washings. ...
answers.google.com/answers/threadview?id=38958 - 9k - En caché - Páginas similares

In the 1960s, as a child in London, I remember many office workers ...- [ Traduzca esta página ]The decline of hat wearing in the late 1960s and early 1970s is traditionally associated with the rise in private car ownership - hats were no longer needed ...
www.guardian.co.uk/notesandqueries/query/0,,-185327,00.html - 37k - En caché - Páginas similares

Mad Hatter Mercury Mystery- [ Traduzca esta página ]The late President John F. Kennedy is thought to have contributed to the decline of hat wearing, as the "first hatless U.S. President" although the First ...
www.seagrant.uconn.edu/HATTER.HTML - 12k - En caché - Páginas similares

www.fashion-era.com/hats-hair/hats_hair_1_wearing_hats_fash... - 42k - En caché - Páginas similares

when hats went out of style/fashion

i prefer your first choice cos a lot of people won't underxstand the sinsombrerismo

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Note added at 16 mins (2008-01-03 20:37:50 GMT)
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the advent of hatlessness

Five Centuries of American Costume - Google Books Result
by R. Turner Wilcox - 2004 - Antiques & Collectibles - 207 pages
Schiaparelli was responsible for two striking fashions of the 'thirties, ... The hatless era of men and women began as early as the late 'twenties, ...
books.google.com/books?isbn=0486436101...

Mike :)





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Note added at 26 mins (2008-01-03 20:48:00 GMT)
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Urban Legends Reference Pages: John F. Kennedy's Hat
They are the people who were shocked to the core when President Kennedy went bareheaded at his inauguration, ushering in a brave new hatless era. ...
www.snopes.com/history/american/jfkhat.asp - Similar pages - Note this
1958 Fashion
... hair was perhaps in the majority, the frequency of hats or wide headbands of velvet, metal or tortoise shell indicated that the hatless era was waning. ...
www.paperpast.com/html/1958_fashion.html - 39k - Cached - Similar pages - Note this
Hats: A History of Fashion in Headwear - Google Books Result
by Hilda Amphlett - 2003 - Health & Fitness - 240 pages
Meanwhile, in our hatless era the men have turned, most successfully and romantically to the adornment of long hair, and some of the women to wigs, ...
books.google.com/books?isbn=0486427463...
Arkansas Times
At one time, Mormon missionaries wore hats, making them even more visible in a hatless era, but they've given that up. The first door they knock on this ...
www.arktimes.com/Articles/ArticleViewer.aspx?ArticleID=7cd4... - 81k - Cached - Similar pages - Note this
StrawHat.org - Montecristi Panama Hat - Beautiful Soft Straw Hat
In the 1960s Ecuador stopped selling as much as it did as fashion imposed the “hatless” era. Today, people of the world still pay thousand for a good panama ...
www.strawhat.org/ - 13k - Cached - Similar pages - Note this
Five Centuries of American Costume - Google Books Result
by R. Turner Wilcox - 2004 - Antiques & Collectibles - 207 pages
The hatless era of men and women began as early as the late 'twenties, a fashion first seen at the resorts in Southern France and Palm Beach. ...
books.google.com/books?isbn=0486436101...
Kapowie Zone: September 2004
I also found it funny that he continued to use his famous "a tip o' the Hatlo hat" tag well into the hatless era of the late 50s and early 60s. ...
kapowiezone.blogspot.com/2004_09_01_archive.html - 131k - Cached - Similar pages - Note this
La Storia dei Pirati
- [ Translate this page ]
Il terzo che trovai fu Jack "Cuore di Pietra" Hatless, era li che si azzuffava con il suo acerrimo nemico, un certo He-Man, un uomo di due metri vestito ...
www.corsaridellestelle.it/storiedipirati.htm - 16k - Cached - Similar pages - Note this
The Cowboy Hat Book - Google Books Result
by Ritch Rand, William Reynolds - 2003 - Art
past the "hatless era" of JFK to the cowboy presidents—Reagan and Bu*h. Also included are more helpful hints of how to ...
books.google.com/books?isbn=1586852582...

another option!

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Note added at 42 minutos (2008-01-03 21:03:36 GMT)
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http://www.lvfashionweek.com/website/e-newz_july21_5.htm

The firm has been one of the great names of British hat making for almost as long. Indeed, it prospered, and in the heyday of hat-wearing, in the late 1800s, the Christy factory in Stockport in northern England extended over twelve acres and had more than 3,000 employees.

the move towards bareheadedness (or bare-headedness) or the movement (if there was one) for bareheadedness

If anything makes a hatmaker's hair stand on end, it is a man who does not wear a hat—especially if he is the President of the U.S. Last week, fearing the national impact of John F. Kennedy's usual hatlessness, the hat industry set out to rescue the nation's impressionable young men (and itself) from the perils of bareheadedness. In an eye-catching, full-page ad in the New York Times appeared a huge portrait of a beatnik so snaggy—and hatless—that no rising young man could afford to look anything like him.

http://www.time.com/time/magazine/article/0,9171,872006,00.h...

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Note added at 53 mins (2008-01-03 21:15:07 GMT)
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or variant of your version:
"...the so-called 'sinsombrerismo' movement in the 1920s and 30s, in/under/during which the fashion was for not wearing a hat"

i think the concept of there being a movement or a new "moda" of not wearing hats needs to be conveyed. Some google hits indicate "sin sombrerismo" was an actual movement or fashion in and of itself, not simply people gradually abandoning the tradition of wearing hats