"Something which has never occurred since time immemorial; a young woman did not fart in her husband's lap."
Ok, it's lame, but it's a Sumerian joke from 1900 BC, regarded as the oldest joke in the world.
I like this one better, from the 1st Century BC
Emperor Augustus was touring his realm and coming across a man who bears a striking resemblance to himself.
Intrigued, he asks the man: "Was your mother at one time in service at the palace?"
The man replies: "No your highness, but my father was."
