I suppose this would be similar to thinking of an experiment that would prove or disprove that some same particular species of spider lives in the rainforest.
The experiment is "look for the spider", and if you find it, then it exists, and if you don't, then you don't really know, but it makes sense to tentatively assume the null hypothesis (that it doesn't exist).
Also, to be more complete, when you've searched the whole forest, several times over, and had a hundred cases of believers saying "there, that's the spider!" and then you caught it and it turned out to be ... not the spider, then you can a) put more confidence on the null hypothesis and b) ignore the next time the believers say "but this time, over there, certainly!".
There is a good argument to be made that the existence of God is also not falsifiable in principle. You could have a super powerful alien capable of destroying entire worlds and causing us to hallucinate in anyway it desires. You could never really trust that an entity claiming to be the creator of the whole universe was telling the truth. Any beings significantly more technologically advanced than us would be practically indistinguishable from a God.
There are two excellent arguments that disprove creator-of-the-universe type gods quite thoroughly. The first is by extrapolation, like above: Everywhere we have looked and thought we'd find godly influence, it turned out to be not so. This has been going on for hundreds of years, so it's safe to assume it's not a fluke. If we can assume that it will continue, then god will retreat further and further the more closely we can look. In the end we will end up with something that a few religious people are already postulating: A being that supposedly created everything and is allmighty, but can never be found because it's actually a total hands-off guy. But then, Nietzsche really killed him, because the argument becomes really simple: A thing can be defined completely by the effects it has upon other things. If it has no effect on anything, then it does not exist. From this follows a) there is no such thing as a thing-in-itself and b) there is no such thing as a no-touching-the-universe-god.
The second is that we know entropy to increase over time. God, however, is a highly ordered state and explaining how the universe went from a high entropy state to a low entropy state, and from high complexity to low complexity turns out to not make the claims more likely or simpler, but the opposite.