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.
I remember my mom getting uptight over the word "sucks", as in "that sucks" or "it really sucked". Literally everyone was saying it, there was no way I could help it lol
Mom used to get angry about me saying something sucks. She explained why it made her angry, and how it referenced a terrible and no-good sex act. I was about 16 at the time, and had already experienced this horrible, no good thing that nobody should do and just felt sorry for dad.