Isn't that awesome? It's a Woot shirt, which means that it's on sale only until such time as it's not in the top 20 sellers on the site and then it gets axed.
I don't know how likely it is for it to get axed this time around because they didn't give us a Friday update on the rankings like they used to/usually do. It's had a good long run, 20 weeks. But I believe it's mathematically possible this will be its last weekend on sale. If it is, your last chance to buy is Monday before midnight Central time.
But buy now and maybe it'll have another week of life. :) Just click the awesome picture.