Here’s an article about trying to find the funniest joke in the world, while I didn’t find the highest ranked joke all that funny, I found the highest ranked british one to be pretty damn funny:
A man goes to the doctor and says: “Doctor, there’s a piece of lettuce sticking out of my bottom.” The doctor asks him to drop his trousers and examines him. The man asks, “Is it serious, doctor?” and the doctor replies, “I’m sorry to tell you but this is just the tip of the iceberg.”