This one is only slightly naughty, but rather long.
In old Småland, there is a village with two churches—one run by a young pastor and the other by an old one. Every Sunday after services, the two pastors met at the local cafe to discuss the spiritual welfare of the village. One Sunday, the younger colleague arrived very late, looking very upset.
"What's wrong?" exclaimed the old pastor, sincerely concerned.
"Someone in my parish stole my bicycle, and I don't know who!" cried the younger man.
"This is how you get your bicycle back," explained the older pastor, who was old enough to know a thing or two about the world. "Next Sunday, give a sermon on the ten commandments. Really lay on the fire and brimstone! Put the fear of God into them, and when you get to "THOU SHALT NOT STEAL!" look out over the congregation and see who is sweating the most—this is the one who stole your bike.
The next Sunday, the pastors met at the cafe at the usual time, the young pastor looking quite composed. "Did you do it?" cried the pastor. "Who stole your bicycle?"
"I gave the sermon alright," said the young pastor. "I really laid in to them, too. People were quaking in the pews. 'You shall have no other gods before, do not make unto thee any graven images...' you know them all of course... And when I got to 'THOU SHALT NOT COMMIT ADULTERY,' I remembered where I left my bike!"