This is hilarious, can somebody fact check this for me? I don’t speak Japanese.

The slang I'm referring to was mid to late 20th century, by that time electronic refrigerators had been the standard for quite a while. Ice boxes were used up until the early 20th. The usage of the word "icebox" in the 40s and 50s was far higher than it had been ever before, which goes against your hypothesis. Far more likely that the slang term arose somewhat independently through metaphor.

Folk etymology is fun and all, but it's not proper linguistics.

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