Here's the problem I see:

If you had a hallucination about seeing Jesus raising the dead and curing lepers so vivid and complete that you were convinced it was real, but years later you tried to teach your child the "ultimate truth" and your child looked for contradicting evidence but it had been so many years later that all the evidence that this was a hallucination had been lost.

Here's another:

If you decided that the world would be a better place if everyone believed in this one miracle-worker whose existence and works you've fabricated out of whole cloth and started teaching everyone about his life and works and fabricating "relics" of his, then years later you were teaching your child about it and the inconsistencies in the "relics" you fabricated (like that it was made thousands of miles away from where you said it was found) have been forgotten in the intervening decades, they might be tempted to believe you.

How about this one:

God, who desires that people believe in and love him, feels that providing a great healer who is obviously supernatural to one particular generation will not damage their faith. Unfortunately, God later changes his mind and later thinks that maybe providing people with convincing evidence of his existence wasn't such a good idea, so he stops providing evidence. Thousands of years later, peoples' faith is waning, but instead of providing the miracles he found so appropriate before, he decides to induce hallucinations in a few people who already believe in him so that they can try to convince people and get rich in the process. A lot of people do follow these few chosen, but a lot don't, too. When the people who don't believe start doing things he doesn't like, he doesn't speak to them directly or provide another obvious miracle to convince them to stop their sinful ways, instead he kills thousands of children in a natural disaster. God is very careful through all this to only do things which could be attributed to nature, though, because unlike in previous generations he doesn't want people to actually have any evidence.

What do you think? 

And why is their behavior wrong?

Why is a 'god' working in such a way that it can be honestly doubted that he existed, when said god wants people to know he existed?

You see, the problem is this: This 'god' creates his people with rational minds, and then works in such a way that their rational minds honestly doubt him.

So the problem  here is that this god is responsible for the outcomes.

If the theist responds by saying "But god wants faith" then you have to ask 1) How you can KNOW this if this god only wants you to believe on faith and 2) why then are we blaming rational people for not believing?

The real problem here is that a 'god' that wants people to know of his existence would simply make his existence known.

Here's a question to ask your friend: Do you have any problems proving you exist? If not, then why do your god have such a problem? 

Refuse to believe? That makes it seem that belief is just a choice. It is not. You can't believe what you don't believe, you're not free to believe whatever you want.

The fact is, the children would have good reason not to believe an incredible claim without any evidence.

The child is not disobedient. The child is rational.

I find it fascinating that disobedience comes up, because this is precisely Dawkins' hypothesis: that irrational belief is born of the drive in children to trust in their parents. 

That's a good idea. Look at all the common myths theistic arguments rely on:

Beliefs are volitional. You can believe whatever you want.

Certain beliefs or disbeliefs are a sin.

In particular, disagreeing with parents is disobedience/sinful. 

Believing without any justification is not only moral, but praiseworthy. (I'll quote the NT here)

The points brought up by Yiab, MisterDax and todangst are good ones. After thinking about it I realize that the problem is that whatever I say in retaliation, no matter how legitimate, can be turned against me; it's the wording thats the enemy here, sort of.

 If I was to tell him that it wasn't a very legit point because the evidence is still missing he would respond by saying "See, you can't know for sure". But I do know for sure. Or as sure as I will ever get that his belief is rediculous.

So unless I come up with a way to prove that the miracles were never performed, it is as if I "lose".

I'm working on a theory to simplify atheist responses to theist arguments.  It seems to me that EVERY theist argument I've heard recently relies on one of two, or maybe three faulty cornerstones:

1) Defense by redefinition: The theist explains away contradictions by claiming that a word is not properly defined, and then not defining it.  

Ex: Theist: God does not experience emotions the way man does.

Atheist: Ok, how does he experience them?

Theist: Not like man.

This is not a definition, or a redefinition.  It is simply avoiding the contradiction by claiming that it doesn't exist.

Note: this encompasses the argument that knowledge can come from sources other than logic, since logic is, by definition, the description of the thought processes that lead to deductive knowledge.  One must redefine knowledge to accept this theist argument!

 2) Defense by Burden of Proof:  This is where the theist claims that he must be proven wrong.  The problem with this becomes self evident when one considers the possibility that the theist is correct.

a) A thing must be proven false before it can be disbelieved.

b) There is no possibility of completely disproving a thing without omniscience.

c) Since humans are not omniscient, nothing can be disproven.

d) Therefore, everything must be believed.

e) Some things are contradictory.

f) Therefore, anything that has a possible contradiction is both true and false.

g) Therefore, knowledge is meaningless.

It gets really nasty when you realize that if a theist is correct, you can also posit that:

Some things are both contradictory and not contradictory.

It gets really nasty from there.

Anyway, I can't think of any theist arguments I've heard that don't eventually reduce to one of those two faulty premises.  Maybe you know of more?

The fatal flaw here is that evidence of super naturalism would be super natural by definition. And so, could not be affected naturally, if at all. Therefore unequivocal evidence of a god would be indestructable to our perceptions and capabilities. If such evidence existed, it would still exist. Even worse, just because the father saw floating pink elephants blowing bubbles, it doesn't mean it actually happened.

Thanks to everyone for advice. He lost. (Or as close as saying "Well what you say make sense but I still BELIEVE..." comes to a loss)