you can't disprove something that is so vague. to pin something down with logic, you must actually have set rules, with which you can argue against. they never do this, cause if they did, you could then possibly disprove their god.
I don't bother with peoples personal definition of a god. The bible clearly defines god (I know christianity so that is what I use, and I have used the biblical version of god for this particular argument) so I just use that definition, and if a someone says they don't define god like, I say ok then you are not christian.
As for disproving something vague, I believe it is possible. As I stated in previous posts, all you need is one single qualifier to decide what something isn't. For instance if something has four traits that it must have in order qualify as something, then it is reasonable to say that if something is missing one or more of those traits then it is not the "something" in question. And if you can prove that it is impossible for something to possess one or more of those traits, then you essentially haven proven that the "something" cannot exist.
It is important to know also, that this doesn't apply to proving something is what it is. If you want to prove something but only know one trait, then you can narrow down the list of things that could be that "something", but this doesn't prove what they are, it proves what they might be. They would also have to meet all the other requirements to be moved into the category of what you are trying to prove. If they don't meet even one, then they are not the "something" that you are looking for.
