Simple answer: The same way that you handle Diwali.
I've been looking over the annual "Christmas debate" posts elsewhere, and doing assorted eye rolls. Here are my basic guidelines:
1. While it may be part of the general culture for many people, it is still a religiously-oriented holiday. The fact that an atheist may still celebrate it doesn't change that. Some people will not want to celebrate it for religious reasons, and that should be respected.
2. Speaking as an observant Jew - I have no problem with other people celebrating Christmas as their holiday. Don't pretend that it is a secular thing on my account. I just want the fact that it is not MY holiday to be respected.
3. If I know for a fact that someone celebrates Christmas, I may wish them a Merry Christmas. Back in September, I also wished my Muslim legal assistant an Eid Mubarak. If I happen to be aware of the holiday that someone is celebrating, I'll give that person holiday wishes when the holiday is actually celebrated.
4. If I don't know whether a person celebrates Christmas, and Dec. 25 is approaching, I will often just say "enjoy your holiday". To me, a government-mandated long weekend = holiday.
5. Chanukkah is not the Jewish Christmas. It is a minor Jewish festival, and it came early this year so it's over. My big holidays are in September/October and April. Nevertheless, I'll accept Chanukkah greetings with a "thank you".
6. If a friendly client happens to wish me Merry Christmas, I smile and say "Same to you." I assume that it was meant in a friendly way. I would only get annoyed if they went on and on about the "war on Christmas" or otherwise got preachy. If they ask specifically about my plans, I either say, "nothing much, we're staying in town", or "we're Jewish, so my husband is working his shift and I'll have Chinese food and a movie with the kids", depending on how much time I have to talk.
7. Yes, Christmas carols do sound nice. However, they are certainly religious, and therefore my kids don't know them. [I'll hum along in secret, just like I do with Duran Duran songs, because they both remind me of my 8th grade Glee Club experience.]
8. Snow is not Christian. Really, it's not. Jingle Bells is not a Christmas song. Winter Wonderland is not a Christmas song. When I once spent Christmas is New Zealand, I discovered that they associated Christmas with the start of summer. I also remember being really disoriented when I visited Bethlehem - in my mind, I also pictured "Oh Little Town of Bethlehem" playing when we visited my grandfather in his chalet in the mountains north of Montreal over the Christmas break, so I thought of the town as being a snow-covered village in Quebec. Needless to say, the hot and dusty Middle Eastern reality was a bit different.
9. No, I don't need to start celebrating Christmas because "I'm in a Christian country now". My family has been here for over 100 years, and we are just as much a part of the country as anyone else. Would I expect my non-Jewish neighbours to start celebrating Passover, just because we live in a predominantly Jewish area?
I had to pinch myself while reading this:
Seriously, people? Lack of a Santa visit to a preschool prompts a "what is this world coming to?" Are there NO real problems in your world (like, say, rampant xenophobia)?
10. Please don't give out "Jesus is the reason for the season" cards unless you are prepared to get a "Pagan worship of the winter solstice is the reason for the season" card back. [I had no idea about this until an evangelical Christan friend told me that she didn't celebrate Christmas because it wasn't actually Jesus' birthday, but was a way of co-opting the Pagan holiday of Yule.]