You can joke about religion without being insultin, for example

PROOF OF THE NON-EXISTENCE OF GOD
The argument goes something like this:

"I refuse to prove that I exist," says God,
"for proof denies faith, and without faith
I am nothing."
"But," says Man, "The Babel fish is a dead
giveaway, isn't it? It could not have
evolved by chance. It proves you exist, and
so therefore, by your own arguments, you
don't. QED."
"Oh dear," says God, "I hadn't thought of
that," and promptly vanished in a puff of
logic.
"Oh, that was easy," says Man, and for an
encore goes on to prove that black is white
and gets himself killed on the next zebra
crossing.

But i have to admit the insulting ones still give me a greater belly laugh

I don't go to mythical places with strange men.
-- Douglas Adams, The Long Dark Tea-Time of the Soul.