Freud had a favourite joke, which is also one of my own favourites.
A young Prince was walking along Oxford Street, when he came face to face with another young man who looked exactly like him. He was so struck by the resemblance that he asked his look-alike 'Did your mother ever work at the palace?'. His double replied 'No, but my father did!'.
I've always liked the jokes in Christmas crackers. Q. Which is the richest country in the world? A. Ireland, because its capital is always Dublin! (doubling)
I mention the above because I've just added another one to my list of favourites. Q. What do you call an underground-train that is filled with scientists? A. A tube of Smarties!