We call someone a Grinch when they shun the holiday spirit and don't follow the winter traditions, such as Janet from HR, who refused to believe you were smoking mistletoe in the bathroom during the office Christmas party. (Note: Please don't smoke mistletoe.)
In any case, accusations of Grinch-hood ignore the fact that the actual Grinch wore a Santa suit -- because sometimes the pettiest, most anti-Christmas messages come in the most cheerful forms.
(Franklin Delano Roosevelt changed the date of Thanksgiving in 1939, and half the country passive-aggressively celebrated the old one anyway. For more on how crazily divided America's pretty much always been, get yourself a De-Textbook.)
Case in point:
4 Woman Aims Christmas Light Middle Finger at Her Neighbor
Faced with the problem of adequately expressing her Christmastime hatred for her next-door neighbor, Sarah Childs went the classy route and flipped her neighbor the bird. Well, her neighbor and everyone else who passes Childs' street at night, because this particular sign-language F-You is made out of Christmas lights -- and it was proudly displayed on the roof of Childs' house:
You should she what she has her manger scene doing.