I never initiate but will respond to adults with "you too" and will repeat back what a child says. Most say Merry Christmas.

"and to you"

Whatever a conversation requires!

If I know what their beliefs are I'll say whatever is appropriate. I most often say Merry Christmas because it's really not a religious holiday anymore anyway. I don't see how buying a kid an Iphone has anything to do with any religious belief.

I say what I think they want to hear what ever that may be .

i have no problem wishing people a Merry Christmas. I just respond in kind with whatever the say. They are just being kind. Why would that piss me off. Christmas means different things to different people, and to some it means nothing at all. To me it means pretty lights.