I always say Merry Chrsitmas and if I know the other people are Jewish or celebrate some other holiday, I'll try to include theirs afterwards.
Nothing wrong with saying Merry or Happy anything anyway you can around the holidays.
I even tell my stepson... Happy Solstice and give a card with that on it, instead of Christmas wishes or cheer. He appreciates it and understands it's not my way, but likes the idea I acknowledge his.
The funny part is.... this is the time of year people celebrate so many forms of the holidays, but they'll all accept Chrsitmas presents without blinking an eye.
We have some Jewish friends who come over some time of the week and we sing Christmas songs and talk about how we celebrate the time and then they tell us what they do, but they seem to like ours better. They also like the sausage products and after eating them.... say oops, I didn't realize.........
..... but they do it year after year.
We know Stu and JoAnn for over 30 years and this just seems to slip their mind. :Big Laugh
Some other very old friends call it 'Three Kings Day' and really don't acknowledge it being Christmas because the way we do it is considered sacrilegious to them, but their kids know it as both ways and much prefer Christmas and Santie Claus.