"And if I'm talking to a Hawai'ian, I say "Mele Kalikimaka". : )"
Sure. Fit the greeting to the person. That's what I do. I'm not sure why people think that an atheist can't wish someone a "Merry Christmas." It doesn't matter what I believe; the greeting is for the receiver of the greeting.
I believe that everyone should be free to hold whatever religious beliefs they wish, and am happy for them in those beliefs. That I do not share them does not mean I should denigrate them.
I can agree with that. Even though I'm a Christian, I still hope my Jewish friends have a Happy Hannukah, etc.