Here's one I heard on t'Internet today.
A Polish former is ploughing his field when he turns up an old oil lamp. He gives the lamp a rub and naturally a genie pops out.
"Thank you for releasing me," says the Genie. "I will now grant you three wishes as a sign of my gratitude."
"I would like a horde of Mongols to invade and pillage Poland and then go home again," says the farmer after thinking for a bit.
"Your wish is granted," says the genie and a horde of Mongols suddenly invades Poland and steals all the farmer's cattle. Then they leave.
"Second wish," says the genie.
"I would like a horde of Mongols to invade and pillage Poland and then go home again," says the farmer." The genie raises an eyebrow but grants the wish. A horde of Mongols suddenly invades Poland and burns down farmer's barn. Then they leave.
"Third wish," says the genie.
"I would like a horde of Mongols to invade and pillage Poland and then go home again," says the farmer." The genie is now looking puzzled but grants the wish. A horde of Mongols suddenly invades Poland andloots the farmer's house and then burns it down. Then they leave.
"OK," says the genie. "I've got to ask, why did you want the Mongols to repeatedly invade Poland?"
"Well, to invade Poland and go home again three times, they have to go through Russia six times."