An agnostic thinks that it is impossible to know with certainty, one way or another, whether a God exists or not. And since most of the Gods people believe in are unfalsifiable, it is technically true. You can be agnostic but still think one is more likely to be true than the other, even though you acknowledge you will never be able to prove it or know with absolute certainty.
this is what I'm talking about, why would you introduce the term agnostic here? I don't know a single atheist who claims that a God can be proven or disproven.
Yeah, it seems often to be used as basically an inoffensive way for someone to say they don't believe in God. Also as far as I can see it's wrong to use it as synonym for a "neutral" view - if you take a neutral view to mean you're just as close to believing God exists as you are to believing he doesn't. Being agnostic (in reference to your belief in a God) only means that you think that we cannot know the truth of a his existence - beyond that an agnostic could lie anywhere believing in God (but not claiming to be able to prove it absolutely) and not believing in God (but not claiming to be able to disprove it absolutely). It does not necessarily mean a "50-50" position.
Although to add a little more; people are absolutely right that lack of evidence does not prove that something is not true. I am listening to music as I type this. Do I have any evidence to give you to back that up? No. But obviously that is not "proof" that I am not listening to music.
Likewise, if there is no evidence for the existence of a particular God, that does not "disprove" that God's existence. However, I do not believe that means that everyone should take a "neutral" view - i.e. say that because there is no evidence to "disprove" God, we should consider it just as likely he exists as does not, or even to start at that position and wait for evidence to push us either towards the negative (atheism) or positive (theism). Because, as most people are quick to point out, there is essentially no such thing as "negative" evidence.
And it is very easy to make claims that can't be disproven. So if you use the "absence of evidence is not evidence of absence" argument to arrive at the conclusion that we should take a "50-50 position", then we should do that for any claim someone makes as long as it can't be falsified. I have a pet lizard that is invisible to everyone else and completely undetectable using any sense or measuring instrument. Technically you can't disprove that - as I said, any lack of evidence arises from my lizard being completely undetectable. But I have zero evidence to actually give you. So what do you think about my lizard? Do you think it's 50-50 that he exists?
Obviously a facetious example, but like I said, taking the view that lack of negative evidence means you should be neutral in your belief of something's existence leads you to some absurd conclusions. That's because there's a problem with using a "neutral" approach and waiting for either positive or "negative" evidence to sway you towards belief or disbelief - that is that although you can have mountains of evidence supporting something, there is a sort of "ceiling bumping" when it comes to the other side; you can't really go much further than just having "no evidence". So claiming that "no evidence" automatically means you should take a neutral view doesn't seem sensible, when that is as far negative as anything can go.
That's why, for me, I'm comfortable putting God into the "I believe he doesn't exist, pending any further evidence" category, along with everything else supernatural. I will not try to "prove" he doesn't exist because, like I said before, I don't really think that's possible when the claims made about him are that he is "outside of the universe", "untestable by science" and such things like that. The only thing that's required for my disbelief is the fact that there is no evidence, or a logical or philosophical argument that (to me) lends any support to the fact that he does. And that's why "arguments for atheism" as they were called, might consist of trying to make a case that "arguments for theism" are inadequate - because it is the lack of adequate arguments or evidence that leads to disbelief. Of course, I am not trying to say that I can state with absolute certainty that God doesn't exist, and if evidence or (even less likely) a new argument came about that seemed good enough to me, I would then end up believing God existed (while still maintaining it was impossible to prove absolutely, unless new evidence did that in which case agnosticism was just plain wrong). But until that time, I'm fine with disbelief.