Calling Buffett's bluff

Warren Buffett, in The New York Times, called for a higher taxes on the mega-rich like himself. Warren, what are you waiting for? An invoice? Get out your checkbook now and donate a few billion to the US Treasury or the IRS. Why wait? I'm sure they won't turn it away. Oh, and remember not to claim  a tax deduction on it as a  charitable donation, there's a  good  multi-billionaire.