This isn’t an actual myth, but in honor of the holidays, I thought I’d post this bit of research submitted by Kenneth Archbold of Mount Vernon, who reports that people there were debating which greeting–Merry Christmas or Happy Christmas–would have been used during George Washington’s time.
From what I’ve been able to find out, “Merry Christmas” is indeed what one was more likely to use at the time, if any greeting was used at all. Different sources trace the origin of the phrase back to different dates, but in each case that I’ve seen, they all pre-date the 18th Century. The casual use of the phrase in Charles Dickens’ “A Christmas Carol” seems to suggest that it was already well-known to the English by the early to mid-19th Century. “Happy Christmas” seems to have originated in the late 19th Century and, in the opinions of some, grew out of the temperance movement in an effort diminish any association of Christmas with the alcohol fueled celebrations of Christmas past (the word “merry” being often associated with drinking, indulgence and raucous celebrations).
If you were to step back in time to 18th-century America, how likely would you have been to hear any greeting at all on Christmas day? As you probably already know, that depended on where exactly you were. If you were in New England, the answer would be none at all since the Puritans had banned the holiday in the mid-17th century, and it wouldn’t be celebrated there again until the early 19th century. The Quakers in Pennsylvania might not have outlawed it, but they didn’t really observe it either. Anglicans, Catholics, Lutherans, etc. on the other hand celebrated Christmas as we might expect with parties, dances, big dinners, decorating with holly and mistletoe (no Christmas tree, though) and good Christmas cheer. An article on the subject is here: http://www.revolutionarywararchives.org/christmasthen.html According to this article, Christmas was celebrated most heartily in the Southern colonies.
So all considered, I think it is appropriate to gladly wish visitors to Mount Vernon and Williamsburg a Merry Christmas.