The following argument is popular:
“I contend that we are both atheists. I just believe in one fewer god than you do. When you understand why you dismiss all the other possible gods, you will understand why I dismiss yours.”
(Vox Day gives two proponents, Dawkins is a third, and Lukeprog at “Common Sense Atheism” makes the argument his epigram)
The argument is a sophistry one could use to prove anything. A parallel example is the quickest proof:
Flag waving American: God bless the USA! The greatest government on Earth!
Anarchist: Actually, you and I are both anarchists.
FWA: No, I love government. I’m nothing like you at all!
Anarchist: That’s not true. You’re an anarchist about Communism, Socialism, Monarchy, Oligarchy, and every other government that has ever existed. I just take things one step further.
Get it? Once you get the swing of this sort of argument, you could prove that Stalin was an anti-communist (since he condemned Trotskyism, Leninism, and innumerable other forms of socialism) or that Adam Smith was against free markets, or that Charles Dickens hated literature (he didn’t have very warm feelings about Thackeray, did he?) And so on ad infinitum.
Aristotle wrote a whole book about such argumentative fool’s gold - the particular mistake in the above is in muddling what is true simply with what is true in some way (the Medieval names for the two are, respectively, the simpliciter and the secundum quid). Confound the two, and you end up contending that theists are kinds of atheists.