Merry Xmas!

Xmas is a sacred holiday, celebrating how cool everything is that has an X in it. e.g. X-rays, Xtreme sports, Professor X, Xylophones, The X-files.

And of course, Gen X.

There's some other religious holiday on the same day, but it doesn't even have an X in it.

Not to be confused with X day, though it is clearly cool by virtue of its X.

The astute observer will note that Xmas also has an X, making it one of the few recursive holidays to celebrate itself.