If you do choose to argue with a theist, you will almost inevitably find yourself under a verbal, personal attack. This will happen because they are on the wrong side of reason but don't know it. They are quite convinced of their "reasoning" because it was programmed into them as children and their thinking is completely canalized--incapable of breaking out of its established channels. (Or it might have been as a result of extreme personal need, in which case their emotional need will rise up and attack you like a demon.) If you find yourself under verbal attack from a theist, you might want to give them a summary of just how insane their beliefs are.
"Only a liar, a fool, or a madman would claim to know the secrets of the universe, which one are you?"
"I have a clue already because you believe that you are immortal and have an invisible friend with magic powers. That sounds like a madman."
"But wait, you also think that 'an invisible magic man in the sky did it' clears up the mystery of the universe. That sounds like a fool."
"On the other hand, you can't even be honest with yourself and judge all claims of the supernatural with similar standards. That sounds like a liar."
"I get it. You're all three."