Here's another one that gets tossed around a bunch and some times people do not have a good answer for it or argument against it.
"Well, I have FAITH that god exists and that's all anyone needs. Why cant you have FAITH?"
I added to it a little but it's the same idea. As an atheist you will find yourself being villainized for not having FAITH when all of their other points have failed you will be thrown this curve ball.
Ask yourself, what is faith? Does it make sense in this context?
The problem of faith stems from a larger problem of the lack of understanding of evidence. What people don't realize is that everything that causes us to believe something is evidence. The light particles that enter my brain through the medium of my eyes and cause an internal image of a well defined and well known to me object are nothing more than evidence that such an object is in front of my eyes. If I had no such evidence, I would see no reason to believe that such an object is there.
For example, the only reason I believe that I am currently typing on a computer is that I can see an image of what I have been previously taught to be a computer in front of me. I can also hear the familiar sound of keys on a keyboard and I can feel what I have learned to be the feeling of typing. Furthermore, these all happen in the correct timing to lead me to believe that I'm not just imagining it all. If I didn't experience these things, I would have no justification for believing that I am typing on a computer.
To try to justify belief in god when the evidence is against it by claiming faith is therefore the same as to try to justify belief that I'm sitting on the beach in Bora Bora when all the evidence points to the fact that I'm sitting here typing away on my computer. Trust me, if I believed that faith could get me to Tahiti, I would definitely give it a try. ; )