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:
What is Less Wrong?
Less Wrong is an online community for discussion of rationality. Topics of interest include decision theory, philosophy, self-improvement, cognitive science, psychology, artificial intelligence, game theory, metamathematics, logic, evolutionary psychology, economics, and the far future.
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.
The thing is, you just accidentally punched downon a vulnerable group. Autistic people constantly struggle with people perceiving them as robotic types who can't appreciate art and stuff (it's not really true at all).
If someone said "it's very niggerish", you'd understand the offense, right? It wouldn't be acceptable if you didn't really mean "niggerish", just traits stereotypically associated with the group being slandered.
So don't use "autist" as an adjective for things that are not in any way autism. It's harmful/hurtfull, and the fact that you basically keep defending it without really realizing what you are doing is why it is not being let go.