I don't wish people a merry Christmas unless they wish me one, and when they do I respond, "And you too." or "You have a merry Christmas too." It's not that I worry about people being of different cultures or even averse to Christmas, it's just not something I feel the need to do. I don't wish people "Happy Thanksgiving" and I have always thought that "Happy Easter" was inappropriate.
I try to avoid shaking hands with people, friends or strangers. It's an anachronism, and I usually want to wipe my hand before and wash it afterward. I don't like to share elevators. I wish grocery clerks who have colds would stay home, and I support mandatory paid sick days from employers.
I have all I can do to put up with the people I love, the affection of strangers holds no interest or fascination for me.