I've heard a few theists say "Hitler was atheist."
In the God delusion, I read this and why it's a bad argument. Basically even if Hitler was an Atheist (ignoring the fact he mentioned in many speeches that he was Christian and that he was doing God's work.) his horrendous acts were not inspired by atheism.
Theists seem to think because we don't follow a moral code supposedly handed to us by a higher power we have are amoral. Basically ignoring the fact that there are laws and standards set by society. Are we really that dumb that we need to have a giant sky-god tell us that killing is wrong? Or do we already know that because its common sense that the world would be a bad place if we went around just killing each other?