I like EhBeth's response best also.
I thought I'd try an analogy (because they always work!
It's like I've woken up in a room with a bunch of people, none of us know how we got there.
On the other side of the room, there's a door.
One guy says "We must not open the door, I dreamed there was a monster in there"
One guy says he feels deep inside that we are under the sea, and if we open the door we'll all die.
Another one says she has a special power that tells her there is a feast waiting for us there.
So I say "First I want you all to admit that none of us knows what's behind that door. Only then can we determine how best to respond to our situation."
They all look at me like I've gone crazy.
So in real life then, in discussions with Christians on the matter of atheism, the first thing one has to do is outline what one does and does not believe and get them to accept that as a valid position to hold.
So far, I've failed to ever get past that first step.