OK, actual peeve, not a pet one:

Hanukkah's been over for ten days. It's past. When you wish me "Merry Christmas and happy Hanukkah" today, you're just saying "I think Hanukkah is Jewish Christmas and can't be bothered to know when it is."

I really much prefer a generic "happy holidays" or a specific "merry Christmas" to a specific-but-wrong inclusion of a holiday that's already past.