Implicating merry_christmas -> christmas.

Reason: It's the most wonderful time of year.

Like happy_birthday, merry_christmas is for every picture with the words "merry christmas" written on it.
Whereas birthday is for pictures in which the birthday is celebrated, there are no clear rules for when christmas should be used. Is santa_costume alone enough? If yes, shouldn't it implicate christmas? Should it be used just like birthday?

-1 because of pictures like post #715069 with no relation to christmas, not even a santa_costume.

Agreed with s1eth, The implication makes sense at a glance but not once you look at all the posts.

Would it make sense for any or all of santa_hat, santa_costume or christmas_tree to have this implication instead?

Hm, I don't think so. Better to leave it to manual tagging. A Santa hat could be sitting in a pile of clothed in an otherwise completely non-Christmas-themed image. Exceptions would be uncommon but enough to warrant doing it manually.

Besides, there's no shortage of santa costume-fetish porn out there, and I'm quite certain there's a lot of it that actually has little to nothing to do with wishing someone a merry Christmas.