I don't think most people misunderstood your post; I think a bigger factor was that the content wasn't seen as particularly novel or interesting. ('My joke alludes to something important!' can only do so much to make up for a rubbish joke.) To the extent they did misunderstand, you can probably do more to prevent such misunderstandings by modifying your own behavior than by telling them to modify theirs. And to the extent you can usefully modify their behavior, using 'stupid' and 'autistic' as terms of abuse isn't an effective way to do it.