when replying that way in any way, on text or actually just saying “cool”. my friends say cool a lot and I really don’t mind it and my partner says it too but some people have thought it was rude and I had a friend say “that’s what I say when I don’t give a damn”.
To be fair, I am also a millennial, but most of my friends were surprised when I told them about that correction I received from the younger generation. I guess that says more about my friends than millennials overall lol