So, once again I will assert that it is provably impossible to empirically disprove the total (universal) existence of god, given that we cannot search the whole universe, and will again assert that the asking of the question is irrelevent, since it is unlikely that god gives a toss.
An atheist is simply someone who does not believe in the existence of any gods. It does not necessarily follow that he or she believes they can prove that no gods exist. The question remains as to why you make such a big deal out of god. Do you always make such a long-winded defense if someone tells you they do not believe in any other one of the infinite possible metaphysical claims out there?
Although an empirical disproof of the existence of god is impossible, that doesn't rule out discounting specific definitions of god a priori.