The supposed 'right not to be offended' was invented by the politically correct crowd as a means of advancing their own social agendas. We can't have public expressions of religion (including such things as wishing people a Merry Christmas) because people not of that faith might be offended by them. Unfortunately, when pushed far enough, the right not to be offended trumps every other right - the right to free speech, press, assembly, religion, etc. If I have to curb what I say because I need to worry that my speech might offend you, then I have lost my freedom of speech. Indeed, freedom of speech presupposes that some people will be offended by what others say; if such offense would never occur, then freedom of speech would never be an issue.
The other principle often raised in this context is that of the "separation of church and state." We can't have public displays of nativity scenes, for example, even if the vast majority of the people in a community want one, because non-believers might be offended, and any public display is seen as a violation of the "separation of church and state." However, such an interpretation of the separation principle is a recent distortion. The meaning of separation of church and state, as originally stated, was that the state had no power to interfere in any way with the public expression of religion. Under the original meaning of the term, a nativity scene in a town square, a valedictorian in a public high school mentioning her faith in Jesus as a source of inspiration, or a prayer said in opening a town meeting would all be expressions of the separation of church and state, not violations of it. The people's right to practice their religion in public was absolute; government had no power to prevent such things. However, in recent years, secularist judges have enforced a new meaning on the concept of separation that is 180 degrees from the meaning attached to it by the Founders.
And, if you think about it, the whole idea that religion should be kept out of the public square and should be practiced only in the privacy of one's home is a very large step toward the outlawing of religious practice entirely. In the most totalitarian anti-religious regimes of all time - Nero's Rome, Stalin's Russia, Mao's China and others - people had the freedom to worship God in the privacy of their own homes as long as nobody found out about it. Who could stop them from doing that? I disturbs me that our society seems to be headed in that same direction, where any public expression of religious faith will be seen as a crime.
Sorry, didn't mean to get off on a rant, but the implications of the whole "Merry Christmas" controversy go way beyond one time of the year, imho...