this is a ridiculous thing to say. Atheists have plenty of people to thank and most of us, whether we celebrate Thanksgiving or not, have all sorts of reasons to feel thankful.
If I were asked what I am thankful for this year, I suppose the first thing that pops into my head is that I feel extremely thankful for the recent church-state victory right here in Mississippi. This sort of thing does not happen often enough, and when it does, it certainly grabs my attention. And of course, I am still thankful for the existence of an atheist movement and a secular movement. The tireless activists working to make our world a better place deserve our thanks today and every day.
On a personal note, I am thankful for having a day off, for not having to celebrate Thanksgiving, and for being reasonably confident that Christianity will not intrude on me today like it has on some prior Thanksgivings. What I most needed this year at this time was a break - a couple days off to unwind, relax, and summon the strength to face the end of the year. This has been a rough year, and I am certainly thankful to have such an opportunity.