Christmas has nothing to do with Christ beyond the church trying to co-opt a pagan holiday - Saturnalia. Which actually precedes the Romans by way of Sumeria amongst other ancient cultures that celebrated it as a winter festival. Believe whatever you like but when you try and foist your beliefs on others then we have a problem. Saying "Happy Holidays" just shows consideration for others who don't believe as you do and levels the field for everyone. Monotheism is nothing more than just another passing phase in mankind's history - just ask the polytheists, animists, totemists, et al. - and we'll all be better off when its behind us as well.
“There is no such thing as a weird human being. It’s just that some people require more understanding than others.” - Tom Robbins