A rabbi and a priest walk into a bar. Neither of them have any money on them. The priest asks the rabbit is he wants a drink. The rabbit asks "How? We have no money". The priest walks up to the bar and orders a drink. The bartender says "That'll be five bucks." The priest says "I already paid you"
"no you didn't"
"yes I did."
"Oh! sorry, I must have forgotten, my memory is going."
The priest walks back over to the rabbi. The rabbi walks over to the bartender and orders the same drink. The bartender asks for a five. The rabbi says "I already paid you"
"No you didn't."
"Yes I did"
"Oh, sorry sir, that's the second time today!"
"Now, can I have the change for that twenty I gave you?"
(I take no credit for inventing this joke as I did not =D)