The one that President Reagan told to Gorby in Iceland (kinda goes like this):
A Russian saved up enough money to buy a new car, so he goes into the Zil dealership and buys one. The dealer says, "Thank you for your business. You can pick up your new Zil on this day ten years from now." As the man is leaving the dealership he turns around and says, "Morning or afternoon?" The dealer replies, "Morning, afternoon; what does it matter?" The man says, "The plumber is coming in the morning."