I beleive the original joke was:
"What do you get if you have somebody that is a Dyslexic, Agnostic, Insomniac?
They stay up all night, wondering if there really is a Dog."
You must keep away from saying 'Atheist' Because an 'Atheist' does NOT beleive in god, in any way shape or form. An Agnostic wonders if there is a god, but is not a true beleiver...
Sorry, just needed to clarify it.