Whoa, Cathy. For you to ASSUME that because someone doesn't celebrate Christmas is because they don't know "Jesus Christ as their Lord and Savior" is COMPLETELY off base. I have been a "Christian" my entire life and I KNOW Yahshua is my salvation. When you find that it says He was born on December 25th in the Bible, let me know, because I know I haven't seen it. Your assumptions were rash and unjust, I don't think that's very "Christ like." That's all I'm going to say about that.
Z.-we don't celebrate Christmas either. It took our families a few years to understand that. They would invite us over or try to give us gifts, but we would gently decline. I think co-workers are going to be a little different. I know what you mean about being uncomfortable. If they know that you don't celebrate Christmas, but still give you gifts, maybe you should just accept them. All of my coworkers respected the fact that I didn't celebrate Christmas, so they didn't give me anything.
If you want to talk more, feel free to message me!