A nobleman decides to join the holy crusades. Concluding his beautiful wife should wear a chastity belt while he is gone, he locks up her nether regions and gives the key to his best friend.
He then tells him, "If I do not return within four years, unlock my wife and set her free to live a normal life."
Then he leaves on horseback and about a half hour later, he sees a cloud of dust behind him. Waiting for it to come closer and sees his best friend. "What's wrong" he asks?
To which his best friend answers, "You gave me the wrong key."