Census from responses:
Eat hats: English, French, Norwegian, Swedish, Danish*, Icelandic, Hungarian, Finnish, Estonian*, Hebrew
Do not eat hats: German, Russian, Spanish, Italian, Polish, Yiddish, Mandarin Chinese
Contradictory data re: hat-eating: Dutch
* Hat may optionally be "old"
Provisional unified theory of hat-eating (highlighted countries eat hats to express an unlikely event has occured)
The major outstanding question here is whether they eat hats in Estonia*. Is this a universal feature of Uralic languages
* Update: YES
It can be dangerous to draw inferences from raw decontextualized data but at this moment, with data from Norway now incorporated, it certainly seems plausible that Scandinavia was ground zero for hat-eating and the trend spread along language affinities from there
Now, you may ask: But then why did hat-eating not catch on among the West Germanic language group? One tentative explanation jumps immediately to mind