DanielLC's comment indicates he at least didn't get the joke. And if people downvote every time they don't laugh, that's a great way to encourage people to not make jokes.
I don't think DanielLC's comment does indicate that. (It could. But I know that for a variety of reasons I have sometimes chosen to treat comic exaggerations at face value despite understanding that they are intended as comic exaggerations, and I don't see any reason to suppose that no one else ever does that.)
For example, what would be inappropriately off topic to post to LessWrong discussion about?
I couldn't find an answer in the FAQ. (Perhaps it'd be worth adding one.) The closest I could find was this:
However "rationality" can be interpreted broadly enough that rational discussion of anything would count, and my experience reading LW is compatible with this interpretation being applied by posters. Indeed my experience seems to suggest that practically everything is on topic; political discussion of certain sorts is frowned upon, but not due to being off topic. People often post about things far removed from the topics of interest. And some of these topics are very broad: it seems that a lot of material about self-improvement is acceptable, for instance.