I heard a complaint about “Muslim, atheistic, Jewish, pagan, etc., friends were complaining about people wishing them ‘Merry Christmas.’” Well, I say “Bah humbug” to complaining that people were automatically assuming that you are Christian. I, myself, am somewhat agnostic on that point, but the point being is most people are just trying to give a cheery greeting. Grumbling about that is sort of politically correct, and in my opinion PC is about as useful as a bump on the head. If you’re offended, don’t grumble at them; instead wish them whatever greeting (Happy Hanukkah, Kwanzaa, etc.) back at them. Spread some good cheer instead of grumbling about assumptions people make.
If you’re really seriously offended, wear a name tag with your designated belief. Happy holidays is just too PC for me and I think PC is for the differentially brained. If most people were really trying to insult you they could do it far better than saying “Merry Christmas!”