Been listening to the most popular radio station in the world. They are based in London.
From time to time, American guests - Leonardo DeCaprio, was one - appear for short interviews. When it ends, the British host, in the manner of the UK, bids his guest a "Happy Christmas," and without fail the American returns with an overly-assertive Merry Christmas.
I suppose it is very much like when MoChassid friends wish him a "Shabbat Shalom," and he raises his voice, arches his eyebrow, and answers, a gut shabus.
Or when Adam weilds his lulav like a spear in the general direction of people who wave their's according to other customs.
Glad to see that the non-Jews have their stupid hang-ups, too.