The burden of proof only falls on those who postulate a positive, not a negative. Or, they have to prove knowledge, not a lack of knowledge. That is how science works.

They cannot. They are both "believers".

Easily.
The person who identifies as the Christian is the Christian whilst I am not.
Differentiation complete.

Quibbling about semantics, "say" or "believe" are two different things.
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I personally can't "say" that gods don't exist, but I can "BELIEVE" 100% that gods don't exist. Same thing about Christians who believe a God exists, they can't "say" 100% that any gods exist, because that would require proof and there is none, but they surely can believe 100%.
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Gods only exist in faith through belief, not in reality. Gods surely exist in faith for believers 100%. For atheists, gods 100% do not exist within their faith and belief system.
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In my mind and in my faith, I am 100% sure that god's don't exist, however I will not attempt to prove that to anyone, so I can not say definitively there are no supernatural gods.

It's only a belief

I need proof, not faith.

There are thousands of known gods. I will say that none of them exist.
So I do not accept the existence of an as yet unknown God as that would seem even less likely. When we say that maybe a god exists, what are we talking about? Many gods were tiny gods. Some gods are claimed to be the only god. Some are claimed to be the creators of everything, some all powerful, some all knowing.
There are an infinite number of things I am not aware of. If someone claims there may be in invisible fairy on my shoulder, should I accede to the possibility or dismiss it as bulldust?

I can’t say 100% but...fewer agnostics go out proselytizing and self-righteously judging. Oops, did I just judge?! My bad.

Neither. Claiming a God does or does not exist 100% are both asserting a claim that can not be falsified. It's the same as saying the invisible pink dragon in my garage exists or does not exist 100%. 2 irrational conclusions. A rational mind rests at the null position, one of disbelief, until such belief can be justified.

So I agree with you.

I am busy preparing my offering to Zeus, and will give this some thought tomorrow, okay?

A specific God? Maybe (not in my case, not yet). A any god? Not really, there are too many possibilities to eliminate all of them.