in which I bend, but I hope don't entirely break, my self-imposed ban on current hot topics

Of Atheists and Holy Days

Do I use the phrase "Happy Christmas"?

No but yes. More often I use "Merry Christmas". You'd need a very fine blade to split that difference.

What do I mean by "Happy Christmas"?

That I hope you will enjoy the time of year that your culture calls Christmas. In countries that have historically been majority-Christian, I often assume that you are part of the majority culture, which uses that C-word. In countries where the dominant culture doesn't have Christian roots, I wouldn't use it; in certain parts of the world I easily might, at the appropriate time of year, say "Happy Diwali" or its cultural counterpart. I see this as a way of showing respect to another culture.

Shouldn't I use "Happy Holidays"?

There's no significant difference. Certain Christians keep pointing out that Christmas should be about Christ, and is only a vocal shortcut for "Christ's Mass". They blissfully ignore the origin of "holiday" as a vocal shortcut for "holy day". Historically, there may have been a time when most people in majority-Christian cultures worked on every day that was not holy, so Sundays and Holy Days came to mean the days when you could rest.  The meaning of "holiday" has changed as more work-free days have been created. Changes to the meanings of words do irritate old people like me, but they cannot really be prevented.

Does it upset me when others use "Happy Christmas" to me?

See above. Christmas and its cards and presents were important parts of the culture where I grew up, quite independent of any religious beliefs I or others held. What can be upsetting about a simple wish for my happiness?

Am I an atheist?

Yes, I am. If you have questions, requests, etc. about it, please be advised that I have already written several pieces attempting to answer such; they are not on this blog, but seek and ye shall find. I don't see any reason to repeat my answers here.