There is a common view that Xmas is an attempt by secular critiques of the Christian faith to remove Christ from the Christmas holiday. I have personally heard many Christians express this view over the years and then be surprised at the truth of the Christmas abreviation.
Xmas is an accepted abreviation of Christmas with 'X' coming from the Greek latter "chi," that happens to be the first letter of the Greek word "Χριστός" that is translated "Christ. "Mas" comes from the Old English word Mass. So Christ-mas.
There are simlar uses as in XP or Chi-Rho that was another sympol for Christ and one of the most early symbols used by Christians.
So don't be offended by the use of Xmas but instead use it as a topic to witness you faith in Christ this Christmas.