it’s been my experience that by far more people are offended by “person with autism”, than by “autistic person”. This is because the former implies that autism is something external to the person, while the latter implies that autism is an important part of who that person is. There is no consensus in this matter; but I’ve been given the impression that while some find “autistic” distasteful, few are offended by it. However, a great many people find “person with autism” extremely offensive, and I’ve been repeatedly told this was, in most cases, preferable. See, for example here and here