"I can prove that God is real...

but first you have to prove that God is not real."

I have had this strategy used on me in a variety of ways.
It means they will claim to have knowledge but refuse to reveal it because you will not answer their (insert impossible question.)

It is at heart an admission that the debater can't prove that God is real, so he puts forth an impossible task to his opponent and avoids conceding his lack of proof.

In a current debate, in which I have asked several questions of my opponent, I was given a prerequiste question, "What is your idea of a Christian?"
The answers to my questions would not be given until his question was answered.

I answered, "There is no one definition of a Christian. There are thousands of sects and all are different. There are many different Christian bibles."

He asked the same question several times more and I gave him the same answer.

He refused to answer any of my questions. I believe it had nothing to do with disliking or not accepting my answer.

He had no intention of answering my questions. He couldn't, not just because any claim of a god is unprovable, but because he could not admit to himself the unprovable nature of gods, so this self protecting, unbeatable strategy is used as a shield.

I have seen this many times and it no longer surprises me that Christians are unable to debate their religion. It is very plain to see that they do not know their religion very well.

These kinds of Christians are what Richard Dawkins tweeted about.
 "Yes yes, there are indeed good Catholics (and good Muslims) all over the world. They're the ones who don't take their religion seriously."

They may have read parts of the bible, but their religious experience is based on a loving Jesus Christ and the modern mythology that has grown from the New Testamant into a sort of whitewashed version.
It goes something like, "Jesus loves me and Jesus is God because Jesus loves me and Jesus is God."

They won't actually debate anything because previous debates have taught them that what they see as proof of God is actually just their feelings. Then they claim victory because, "You're a sinner and a tool of Satan and you're going to Hell!"

It's getting harder to find an honest debate these days.
I'm starting to think that if I asked a Christian how his day was going, he'd fake a nose bleed to get away from me