Seems like we waste a lot of time & stress during December trying to figure out just what to say to people to convey our wish that they have a joyous holiday no matter how he or she may choose to celebrate it (or not celebrate it, as the case may be.) So, I have a modest proposal that might just alleviate some of the headaches.
If you're not sure whether Joe in the cubicle next to you or Susie the barista celebrates Christmas, Hanukkah, Kwanzaa, Festivus or nothing at all, but still want to say something, say "Waffles."
Think about it. Waffles are an inherently happy food. They're fun to make, fun to eat and bad things rarely happen when they're part of the menu. When people break up, they go out for dinner. No one gets dumped over waffles.
So the next time you're twisting yourself into a mental pretzel (also a fun food) trying to convey holiday cheer without potentially ticking off a relative stranger, just give them a big ol' grin and say "Waffles."