An atheist cannot celebrate Christmas, but X-mas is A-Okay!
It's not about god or the savior or anything like that, It's about being a good person that gives to and cares for the world and the people in it. Only celebrate it if you believe in that, not for the presents.
Over the last several years, I have asked family to not give me gifts at xmas. I have enough stuff, I would rather celebrate the death/birth of someone more recent, and I am a little too old to care about the stuff under the tree unless it is true plasma rifle,,;p)
So far it has not worked. My mother goes all out, with a big box of stuff for everyone that shows up at xmas eve. We do have a nice dinner, which I always look forward to, but is now small and dad passed sometime ago. Most of the kids have gone off on their own lives, spread over the north American continent. Mom has mostly given up on religion, it just does not seem to do her any good.