This little inspiration came sort of spontaneously about a week ago when I was talking to a Christian guy: he said to me.. 'if you believe in God..yak..yak' So I replied that 'I cannot prove that I believe in God so I must be an atheist; and how about you.. can you prove that you believe in God.. if he does exist?' He could not find a loophole through that one so I teased him that he's probably always been an atheist even if he always considered himself a believer. I tossed the thing around a bit and the most qualified response I could get was "proof" of belief by faith which is not proving that one does believe in god. So that must mean EVERYBODY is an atheist or agnostic until someone can demonstrate proof that they DO believe.
On the other hand I think I can prove that I believe there is no god by saying that there is absolutely no need for a god.