Well, to have all the decorations and such and not use the term to be politically correct makes no sense to me. If it's a Christmas pride or something... Honestly though like a store greeter, I think the population is too diverse to use holiday terms at all. It just isn't necessary.
I'm a non-denom Christian (although I don't like how the term is used now-a-days) and I don't celebrate Christmas, nor do I even use the phrase Merry Christmas even if I know someone else is celebrating it (not going to go into why b/c the thread would turn religious). I don't wish anybody a happy holiday no matter what holiday it is except for Thanksgiving or birthdays because those are the ones I celebrate. If they were going to go celebrate and have a nice time, then I'd say have a good time...
However, if somebody sends a card or something for whatever holiday, I am happy that they thought of me.
If somebody says Happy (insert holiday here), I either just don't say anything or say thank you. If somebody was close to me and knew darn well that I didn't celebrate and why and still kept saying Happy (insert holiday here), then I might start to get irritated.