The Seattle Windshield Pitting Epidemic

In 1954 in Washington State it was discovered in Bellingham, which is a suburb north of Seattle, that a number of windshields were oddly pitted. It was thought to be the work of vandals but the pitting continued spreading like a disease heading steadily south towards Seattle itself. It was too widespread and too rapid to have been the work of vandals and numerous, other causes were considered and dismissed. Old cars were particularly vulnerable. There was a sort of hysteria about it. in the end, as described in a fairly short, fun, and detailed article Neatorama reprinted from Uncle John's Slightly Irregular Bathroom Reader:

The Seattle Windshield Pitting Epidemic of 1954 became a textbook example of collective delusion, sometimes referred to as "mass hysteria." To this day, sociologists and psychologists refer to the incident in their courses and writings alongside similar events, such as Orson Welles' War of the Worlds Martian invasion panic of 1938, and sightings of the "Jersey Devil" in 1909.

The Seattle pitting incident has all the key factors, including ambiguity, the spread of rumors and false but plausible beliefs, mass media influence, recent geopolitical events, and the reinforcement of false beliefs by authority figures (in this case, the police, military, and political figures). This combination of factors -added to the simple fact that for the first time people actually looked at their windshields instead of through them- caused the hubbub. No vandals. No atomic fallout. No sand fleas. No cosmic rays. No electronic oscillations. Just a bunch of window dings that were there from the start.

Collective delusions, I would suggest, are not that uncommon. They range from blowing on video game cartridges to make them work to believing that if you believe you'll go to heaven. Well ... there were witches, you know, in Salem.