Relax. It is a paper coffee cup. Starbucks is under no obligation to print a Christmas greeting on their cup. That is not a "war on Christmas". The cups are red, the logo green. Last year the paper cups from the coffee giant had snowflakes, not exactly a Christmas message either. This is a business. If you have objections to a plain red cup, and I cannot really imagine why you would, then buy your morning brew down at the gas station. I bet they won't have "Christmas" cups either.
I further posit the very people who are up in arms over this manufactured controversy would throw an even bigger fit over anyone who printed Hanukkah or a Ramadan message on their cup, claiming they don't want Islam shoved down their throat. And no, I don't know what a Ramadan message would look like, you are missing the point.