What makes an atheist an atheist?

His tail.

We can't disbelieve in religion. Religion exists. Quite a number of them, actually. =p

Fact is, we are all born atheists. Religion is learned. Some atheists are simply never indoctrinated into any religion, although it's virtually impossible to live in this society without at least being exposed (religious people often wrongly assume that if someone is an atheist, they've never set foot inside a church, which is almost always incorrect).

However, the majority of atheists WERE raised to have some sort of religion or other, and through life experience, education, or personal introspection have come to the conclusion of atheism. The paths we've taken vary as much as the individuals do themselves. For example, my husband was raised Weslyan, was "straight edge" as a teen, which led to an interest in philosophy which inevitably led to atheistic philosophers, then atheism itself.

I, on the other hand, was not raised religiously, so my coming to atheism was earlier and simpler than my husband. For me, the notion of deities and other supernatural phenomenon just doesn't make sense. I stopped believing in Santa Claus, the Easter Bunny, and other magical things as a child, so why would I believe in magic is a grown up?

Atheist means lack of belief in deities. That's all. There are other spiritual paths to follow.

It's a lack of belief in deities, and that is because believing anything for which there is absolutely no evidence seems completely nonsensical to me.

It's really quite simple. Atheists see no definitive proof of the existence of a Supreme Being, so they don't believe one exists.

Honesty.

Logic.

Acknowledging reality.

we like to do our own free thinking.

I will not have some poor guy that does not know any more than me, tell me how I should live my life, every sunday morning.

He tells me I am a sinner while he is molesting 9 year old boys?

Right.

Not believing in any god. Not really sure what else you might be going for here.

I just don't. I know in my heart that there is NO god/diety. It is probably the same way you know that their is a god for you.