I know Christmas has come and gone, but this bothers me so much that I don't want to go another year without getting it off my chest. Every December, I find myself in a lot of situations where someone who is obviously not Christian — my cab driver wearing a Sikh turban, for example — wishes me a Merry Christmas. If I don't respond back with, "Merry Christmas," I feel rude, but if I do, I feel disingenuous. I'm all for wishing a Merry Christmas to people who actually celebrate, but why this farce between non-Christians? What is the appropriate response when I find myself in this situation?
I firmly believe that the "holiday season" is a time for Jews in America to find ways not to take themselves or the proliferation of Christianity masquerading as American culture too seriously. I can't speak for Americans of any other religion, but for approximately one month out of every year, I think it's OK, and even appropriate, for us to accept the fact that the vast majority of our fellow Americans are celebrating a holiday that we aren't.
When someone says, "Merry Christmas," to me, I often say, "You, too," or "Happy holidays," just in case they're not celebrating Christmas — though I suspect that if someone says it to me, they're celebrating themselves. In the case of your cab driver and others who are definitely not Christian, I would view their use of the greeting as a way to integrate themselves into mainstream American society. Though I've never been in the situation myself, I can imagine why a non-Christian and/or non-American-born cab driver would want to appear as savvy about American culture as possible — comfort and camaraderie with riders, possibly leading to a better experience for everyone involved and maybe a bigger tip. I can also imagine why a non-Christian and/or non-American-born anyone living in America would seek out common ground with Christmas-celebrating Americans.
There are all kinds of books and articles about how racial identity has affected Jews in America, but the current common understanding is that most Ashkenazi Jews can "pass" as white. Your cab driver in a turban, or anyone in a variety of other religiously identified garb, probably doesn't have the luxury of passing, while you probably do. (I know a variety of assumptions are going into this response, so if I'm wrong about any of them, hopefully I'm still providing a perspective that's helpful, even if the specifics are off.) When you can easily be mistaken for a member of the mainstream majority, it's easier to be indignant when you're mistaken for a member of the mainstream majority. When you can't be mistaken as such, it makes sense to ingratiate yourself to that majority wherever you can.
All of this is a lot of pseudo-sociological circles around my simple answer: Say, "Merry Christmas," or "Happy holidays," or whatever you want that's polite and reflects the same spirit of peace on earth/goodwill towards men (and women!) as the greeter shared with you. It may feel like a farce, and sure, on one level it's a totally arbitrary adoption of the dominant culture's expectations. On another level, maybe it's a chance to share a friendly moment, maybe with a wink. If you really can't stand the whole exchange, go ahead and say, "Actually, I don't celebrate Christmas, and I don't think you do either, but have a nice night." But I don't think that will be more satisfying. You could always try to preempt the inevitable, "Merry Christmas," with your own "Happy holidays," then wait to see how the other party responds. At least for now, you have almost a year before you have to worry about this again.
Until then, be well,