This is sensible, except "pig" can't be taken literally when talking about a human.
> educated people will take everything you say literally and turn into missionaries
On the other hand, "Autistic" can and is taken literally regularly. So it feels pretty disingenuous for you to expect "educated people" to determine and keep track of how YOU specifically use the phrase compared to all the other people in their lives.
And if one of the people reading/hearing what you say IS autistic, their experience of others using the phrase is probably not as light-hearted as yours. There are plenty of people out there who DO mean it literally. So it is entirely up to the person reading/hearing the comment to make that determination.
You want to blast people in a professional setting who can't string together sentences, go for it. But describing them in a way that CAN be taken literally will cause problems.
TL;DR: My suggestion is to stick to "bad words" that people can't be born with.