Here are a few of my favorite theist arguments, and my usual rebuttals. Please feel free to point your favorite theists to this post when they utter one of these gems.
"Atheism is a belief."
I do not believe in Atheism.
Atheism is not a belief or a belief system. It's not a matter of faith, it's the lack thereof. As a matter of fact, for me, it isn't even just the lack of faith or belief. It's a matter of following the evidence. It's critical thinking.
Put simply, my lack of belief is a direct result of there being no magic sky genie in which to believe.
For further evidence, see the rather profound fact that despite my long-running Atheism, no god has seen fit to smite me for not loving him.
Atheism is a belief like clear is a color.
"If my faith is a result of geography, and you're in the same geographic location, how come you're an Atheist and I know the truth?"
I love this one. First of all, you don't know the truth. You have a belief founded in an extraordinary claim, backed by precisely zero evidence. Nada. Zilch. Not half a fucking iota. This extraordinary claim would require extraordinary evidence to even be considered a viable hypothesis. You, being the claimant, are under the obligation to provide same, where as I, the person to whom you're trying to show the light, am obligated only to take the evidence provided, and weigh it objectively.
I can objectively say that your extraordinary lack of evidence leads the clear-minded, critically thinking person to one provable conclusion: it's bullshit.
"A few hundred years ago, you wouldn't be an Atheist."
A few hundred years ago, you'd have burned me at the stake for heresy. That doesn't mean I wouldn't be an atheist, just that I wouldn't be loud about it.
"Science can't explain everything."
Despite the fact that science hasn't explained everything, everything does in fact have a scientific explanation. The amazing thing about science is that it's a method for knowledge seeking. It seeks to find the truth, not justify what's convenient. To put it more succinctly, science is the way we find the answer, not the answer itself.
I hope this clears up some things for you people out there. Please, if you have any questions about Atheism, or you're a "closeted" Atheist looking for support, don't hesitate to contact me.
I don't always know the answer, but I do know how to get it.