We all agree on that for example pigs, or sheep, can't fly. Why do we agree on that? Have we ever seen any proof of this? Have someone ever made any scientific experiments on the flying abilities of these animals? No, because we don't need to. No one has made the claim that these animals actually can fly. Put in another way: We assume with certainty; we KNOW intuitively that pigs and sheep can't fly. We don't need any hard evidence for it. We just know. It's the same for me with God, I know that God does not exist. All my senses, all my knowledge of the world and of history, my logic and common sense, everything tells me that the very idea of a God (or gods) is nonsense.
The very idea of an omnipotent God in the sky is based on bronce-age man's primitive superstitions and fantasies, at a time in human history when no science existed and the world was an all magical, incomprehencible and dangerous place.
The burden of proof is on the part making the claim. Atheists claim nothing; it's the believers who make the claim that there exist a God. And they have failed for two millennia to produce even one tiny piece of evidence (or slightest probability) for their claim. It is time to grow up and live in the real world.
A quite common reaction one gets from Christians as a non-believer, is that you are supposed to show respect of their delusions. Well, do you really? Respect is not something you can give or take; respect is something you've got to earn. You can respect a person for his or her courage or achievements, for their skills or their unselfish conduct. But, you do not respect people for their crazy delusions. Do you? A quick glance at the bloody history of the Christian Church and their representatives, it becomes obvious that the Church certainly hasn't deserved any respect from anyone. Everywhere wars have been waged, where there was burning, ravaging and spilling of innocent blood, the Christian Church was present. And always taking part on the side of the strong and mighty against the poor and weak.
As a non-believer you sometimes get the question "If there's no god, who created the world then??" or "The world is so beautiful and everything seems so appropriate and perfect that someone must have created it." That's a silly statement, since according to the same logic you could argue that: "Someone capable of creating such a perfect world have to be even more perfect, and then there has to be someone who created him (or her..it whatever)."
The great Norwegian poet, writer (and atheist) Arnulf Øverland once received a letter from a Christian who couldn't believe that such a great poet as him didn't believe in God. He wrote: "I assume that you have common sense. When you see a car in the street, then you know, that that car hasn't created itself " Øverland answered: "The thought is correct and I must accept its consequence: If I see a God in the street, then I know he didn't create himself."