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
@mcc this kinda stuff tends to be areal, not genetic. The presence in Finnish and Hungarian makes me think the French is the original, but that's just a hunch.
EDIT: no, the Finnish is more likely from the Swedish. I'd still bet on the French being the original though.