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Nobody says it anymore
(startrek.website)
I've heard it explained that "hey" used to be more of an urgent way to get someone's attention, rather than a casual "hello" like it is now, so it sounded rude to some older folks.
Isn’t that just Swedish for “hello”, brought here by Swedish immigrants?
No, it's been in English since Old English, but is cognate with Swedish hej.
Hej is definitely Swedish for hello. Not sure about the etymology of hey in America but it certainly makes sense.
I think people were mostly bothered by it when used to get someone's attention... For example, as a substitute for "excuse me" or using a person's name.