<The best, most non-confrontational, and most sensible rebuttal I've seen was written by WEB himself. I can't find it,>

Buffett has responded to this silliness on multiple occasions...

"It's sort of a touching response to a $1.3 trillion dollar deficit. The first person to come up with that was Senator McConnell (R-KY).
It's sort of astounding to me that somebody that has the responsibility of being the minority leader in the Senate would think that you attack a $1.3 trillion deficit
by asking for voluntary contributions. Since he did, I offered to triple his. That's a side show. The real problem we have is we're taking in too little money and we're spending too much.
That's not going to be solved by voluntary contributions. What we need is a policy, a real tax policy." ~Warren Buffett

Buffett also emphasized that his commitment to matching all Republican donations to Treasury coffers is a "firm offer."

businessinsider.com - Warren buffett responded to chris christie telling him to just shut up about taxes