The problem is, theists (some more then others) won't believe me because they always argue from the note that there IS a god.
Just between you and me: it's good practice for an atheist to every once in a while construct theories from that very same note that there IS a god. Sadly, to me theories constructed using this notice seem equelly weak as a theist's arguments.
To prove god doesn't exist I would have to tell you people "stop thinkin as christians, start thinkin "there's this god guy". It helps, and also prevents christians, muslims, jews, mormons, hindu's and (*laughing*) scientologists from attacking each other. Now that we're there, think for a sec that it's completely impossible for a being existing PRIOR to the creation of the universe, as no matter exists yet for that being to consist of. Argueing that this being is exempt from such laws is like saying that being doesn't exist at all. Saying "then what about that big bang thing?".
Here is a nice image from Wikipedia to comment on this. As you see, the universe came forth from this little dot (the singularity), and as physicists all agree these days, everything we know and love about the llaws that dictate how matter behaves mean NOTHING in one of those things. Because of this 'yeah.. anything can happen in there' theory, it isn't necessary for any matter to exist prior to this event, other then the singularity, which isn't matter. So there is a very big difference regarding the question "what was there before the universe was created?" from a scientific and a theist stand point.
Secondly, if god knows everything (he did give us free will, BUT knows what we're going to do anyway), he will have known when he created the universe, that I would be typing this. Since he's had sooo much time to create evidence, why isn't it there right now? God could've easily arranged a bunch of stars to spell out the words "God is here, dawgs" or something. The fact that god was either too lazy or unable to do this would, for me, mean that he isn't actually worth worshipping. A god not worth worshipping essentially doesn't exist.
Evil. Lets talk about evil. I'm going to keep this very short:
The problem of evil arises from the supposition that a perfectly good god would not have created a world containing evil, or would not permit its continued existence in the world, and that an omniscient and omnipotent god should be able to arrange the world according to his intentions. Since evil manifestly exists, it would seem that a god intends it to exist. Therefore such a god is either not perfectly good, not omniscient, or not omnipotent. With the further premise that if a god exists, it must be perfectly good, omniscient, and omnipotent, one can conclude from the existence of evil that no god exists.
- Wikipedia (I got tired, and I'm not an omnipotent diety, but this is the theory I had in mind).
You will now counter this, I suspect. To me, your arguments will seem entirely illogical. Even if I think, just for a wee sec, that god exists. Thinking that doesn't make the arguments I've read here any more logical. If this is because god isn't logical, I direct ye to Upsilon's post regarding god and logic.
Attempt to prove the non-existance of god to theists #534534535 (trying to prove god doesn't exist to people who haven't made up their mind yet usually succeeds within two tries. Really, I've converted people)