Chastity Belt

A man decided to march in the holy crusades. Concluding that his 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 tells him, “If I do not return within four years, unlock my wife and set her free to live a normal life.”
So, the husband leaves on horseback and about a half hour later, he sees a cloud of dust behind him. He waits for it to come closer and sees his best friend. “What's wrong?' ” he asks.

“You gave me the wrong key!”