My 5th-Grader thought the following joke was hilarious enough to repeat it to the rest of the household

Q: Why did I have to go to the dance with a prune?
A: Because I couldn’t find a date.

If you choose to unpack the joke at all it stops being as funny. And of course if you unpacked it far enough it could stop being funny at all, mostly because “prune” has all sorts of euphemistic social, relationships, sexual, age and even age-related alimentary-canal overtones.

At least in English. At least in Anglo-American English. And not just because other languages and cultures my not use the word “date” to mean “arranged encounter with existing or prospective romantic intent.”

Prunes are dried out. Prunes are wrinkly, stiff, even leathery. With that in mind saying “I couldn’t find a date so I went with a prune” implies you’re going way past anything as tepid as “settling:” in colloquial English prunes are literally “the pits!”

Of course except for maybe the leathery part pretty much everything you can say about a prune is equally true of dates. Dried? Check. Wrinkled? Check. Has pits? Check. And you could make a pretty good case that while a date isn’t leathery like a prune is their weird, almost brittle translucent husks don’t exactly evoke youth, health, beauty, or vigor.

In other languages and other cultures and even sub-cultures… even different contexts in primary North American culture, of course, the correspondence between prunes and dates is entirely superficial such that with any amount of unpacking the joke would still be just as funny, or agonizingly corny, if you substituted dried apricots, raisins, or (ahem!) figs for prunes.

Which is, of course, exactly how my 5th grader saw it.

If you’re a seriously desperate nerd social theorist you may already have read John Allen Paulos’ Mathematics and Humor: A Study of the Logic of Humor, which includes the excellent point that a great deal of humor is a product of unexpected disjoint sets. Especially puns and other non-sequitur punchlines were the implied axioms are different from the actual ones.

(My most favorite sex joke ever, which I love repeating, is an excellent example of unexpectedly-overlapping axiom humor: Q: What happened to the couple who couldn’t tell the difference between KY Jelly and window putty? A: Their windows fell out.)

Update: For at least some context see also Re-Branding the Prune at Sociological Images.