I think the closest thing to a proof of atheism I have run across is the argument from non cognativism. It's not a proof, but it is very formulaic and priori.

There are three attributes of existants which concern us particularly, these being:
A) Primary Attributes
B) Secondary Attributes
C) Relational Attributes.
B as well as C are dependent upon and must be related to an existant’s A in order to be considered meaningful.
The term “God” lacks a positively identified A.
Because of this, the term “God” holds no justified A, B, or C. (From 2)
However, an attribute-less term (a term lacking A, B, and C) is meaningless.
Therefore, the term “God” is meaningless. (From 3, 4, 5)
Therefore, the god-concept is invalid.

The Argument From Non-Cognitivism

In the roughest of terms, this arguement makes a good case that God is a philosophically bankrupt term because it is too vague, and defined by what it isn't rather than what it is.

I think it's a strong position, and I think the original poster in this thread puts it on display. He offers two possible alternative gods, both of which are so vague, they can hardly be destinguished from each other, even though that is exactly what he is trying to do.

This arguement is a good one to whip out when one runs into the brick wall of "God is beyond logic" "God can't be put into a test tube" or "God exists outside of reality". If those things are true, especially the later, then god either doesn't exist at all or we should all becom apatheists.