Here's one I heard down the battle cruiser the other day..
An old man and his grandson Johnny are on the way back from the park one day when Johnney turns to the old man and asks, "Grand Pa, do you believe in God?".
The old man replies "Yes, Johnny I do. Now and again when I wake up in the middle of night and want to go for a wee he turns the light on for me. He's a really nice guy like that."
When they arrive back at the old man's house Johnny turns to his Grand Ma and asks the same question. "Grand Ma do you believe in God? Grand Pa does; apparently if he needs a wee in the middle of the night he turns the light on for him...".
"Oh no" says Grand Ma, "..he's been weeing in the fridge again!"