I called myself agnostic for a long time since it's true that no one knows for sure whether or not that there's a god. At one point, though, I just had to ask why I was even labeling myself that. I wouldn't describe myself uncertain when it comes to unicorns. Could they theoretically exist? Sure. But since I haven't seen any observable evidence of a unicorn, I'd say that I don't believe they exist. Since I haven't seen any observable evidence of god existing, I'd have to wager that a god doesn't exist. Therefore, I'm atheist. The burden of proof lies on the claimer of something existing, not on someone requesting such proof. Most "agnostics" just don't like how certain atheists act; they're actually atheist themselves.