The harmless surprise hypothesis fits my data pretty well. But are you sure repetition-based humor isn't just conditioning people to laugh at a certain thing (catch-phrase or a situation)?
On the other hand, butt-of-a-joke hypothesis also sounds plausible.
The Open Thread posted at the beginning of the month has gotten really, really big, so I've gone ahead and made another one. Post your new discussions here!
This thread is for the discussion of Less Wrong topics that have not appeared in recent posts. If a discussion gets unwieldy, celebrate by turning it into a top-level post.