I do not understand why some people have to manufacture controversy. I am not offended by people who say "happy holidays" or "season's greetings". People are just trying to be nice and not be religion-specific. There is nothing wrong with that.
You are not fighting on the front lines in the "war on Christmas". You are buying a pre-made turkey sandwich at H-E-B, and the cashier is trying to be polite. He doesn't care that you believe one way or another. He was just told to say "Happy Holidays" to the customers. Don't be a jerk and sternly say "Don't you mean 'Merry Christmas?'", because that makes you look like a jackass. Stop it.
I would just like to say that one could call me a Christian by my core beliefs. I tend to disagree with the way that most Christians go about pushing their religion in people's faces, so I might not be a "good" Christian by some standards.
On a side note: Is it awful that I enjoy secular Christmas songs more than religious ones? I would rather hear "Jingle Bell Rock" than "Away In A Manger". I'm obviously a terrible person who is going to Hell.
Everyone just RELAX and enjoy the spirit of the holidays, whatever that might be for you and your family. Season's greetings to you all.