What’s worse than the fashion police? A fashion mob. Throughout history, social norms have always helped dictate personal styles. But as arbitrary as these taboos can be, they’re sometimes enforced with violence—as Yankee straw hat fanciers once learned the hard way.

Summer’s end in the late 19th and early 20th centuries meant that men had to retire these caps until spring. By unwritten rule standards, this one was quite specific—September 15th (aka “Felt Hat Day”) was the universally-accepted deadline. As the New York Times only half-jokingly explained, any man who wore a straw hat after this date “may even be a Bolshevik, a communal enemy, a potential subverter of the social order.” Exactly eight months later, on May 15—but not a moment before—a fellow could again don his straw hat, safe from ridicule.

Few cities took this mandate more seriously than the appearance-conscious Big Apple. For years, street-smart New Yorkers knew better than to get caught wearing a straw hat out of season. Doing so, they found, all but guaranteed that some mischievous kid would snatch the offending headgear and stomp it flat.

This obnoxious tradition became downright dangerous in 1922. On September 13 [PDF], the coast was supposed to be clear. But without warning, several youngsters got a head start on their annual hat-nabbing. And the madness was just beginning. “[Scores] of rowdies on the east side and in other parts of the city started smashing hats,” the Times reported, “police reserves were called out, straw hat bonfires were started, and seven men were convicted of disorderly conduct in the Men’s Night Court.”

Such carnage spilled over into the next three days, which featured dozens of new arrests. NYC police officers were told to be on guard for “hat-hunting hoodlums” and did so with extreme prejudice—upon capturing a few young perpetrators, one Lieutenant even “invited the boys’ fathers to come to the station and spank them.”

These attackers frequently came armed. To make the job of ripping into lids easier, many carried sticks studded with nails, often leaving victims with serious injuries.

The dust finally settled later that month, but the custom that started this whole mess lived on for a while longer—in 1924, one man actually died while avenging his straw hat. The following year, President Calvin Coolidge was spotted wearing one on September 18—a scandalous move which received front page coverage from the Times.