A priest and a rabbi are walking down the street together, and they both want a drink, but they have no money on them. The priest says, "I've got an idea how to get us some free drinks." He walks in alone and the rabbi stands at the door and watches.
The priest orders a drink, drinks it, and then the bartender gives him his tab. The priest says, "But my son, I've already paid for the drink." The bartender says, "I'm terribly sorry, father, but it's really busy in here and I must have forgotten." The rabbi walks in and orders a drink. After he drinks it, the bartender gives him the tab, and the rabbi says, "Son, I paid you when I ordered the drink." The bartender says, "I'm terribly sorry, rabbi, I don't know what's wrong with me, but that's the second time that happened to me today."
The rabbi says, "That's okay, son, no offence taken. Now, just give me change for the twenty I gave you, and I'll be on my way."