The Merry Pranksters
Ah, these yokels. A group of hyperintellectual existential philosophers, the Merry Pranksters believe that humor is central to living life, in spite of the fact that they all take their intellectual selves as seriously as a heart attack. They're known to often share a chuckle or guffaw over everything from slapstick humor to a good limerick about phenomenology (i.e., "There once was a man who just thought / Who believed in all he was taught / 'Til he got out of bed, hit himself on the head / And realized that life was more than just read"—or something like that).
J.P.S. founded the organization in college (of course) after he pulled off a hilarious prank around Charles Lindbergh's New York-Paris flights. Sartre and his fellow jokers contacted the media and told them that Lindbergh was about to be granted an honorary degree from the famously brainy École Normale. All sorts of newspapers rolled over only to find that it was a Lindbergh double. You kind of had to be there…
Plato and Aristotle
These two godfathers of Western thought would have been members if they had been there, as they loved jokes that made other people look stupid—they called it "superiority humor," because they loved laughing at someone else's woes. Needless, to say, they're not in the group today because they're, well, dead. But we're also betting Sartre might have had a few nasty things to say about their joining, what with their my-way-or-the-highway tendencies. And since he's the founder, well, he gets the final say.
The group thought that it could handle him but then Siggie just became too annoying. He was a member for a while, but they just didn't think the same things were funny. Plus, Freud sees laughing as a way of releasing "psychic tension," which is just totally missing the point. So Freud. Not everything has to mean something—sheesh.
Henri believes that humor's all about expectations that come up big zeroes, revealing nothing. He and Sartre have had a few skirmishes about the idea of "nothing," but so far they've been able to work through it and have a good laugh about the whole thing.