If someone makes it clear with their body language and words that they aren't interested in you, then don't try to come onto them.
If someone is clearly interested in you, it's OK to try to come onto them.
It's not the other person's fault if they aren't interested in you and aren't comfortable with you crossing the line with unwanted compliments.
The fact that this even needs to be explained is proof that these people literally have autism. They genuinely need to be put in fucking classes to learn basic social skills, because they clearly are unable to understand cues and norms.