What is the greatest joke ever told?

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Academics have unearthed what they believe to be the world's oldest jokes and concluded that humour has changed very little. Human beings have always laughed at farts, and "stupid people" just as we do today, said Dr. Paul McDonald from Wolverhampton University. Britain's "oldest joke", discovered in the Codex Exoniensis, a 10th century book of Anglo-Saxon poetry held at Exeter Cathedral, reads: "What hangs at a man's thigh and wants to poke the hole that it's often poked before?' Answer: A key." Egyptians were telling jokes even earlier, according to researchers. One gag, which pre-dates Christ, reads: "Something which has never occurred since time immemorial: a young woman did not fart in her husband's lap". Is a gag's content most important or its delivery? Have any jokes offended you? Or shouldn't humour be taken too seriously? What is the greatest joke you have ever heard?