It's rude to call someone "an autistic." They are people with autism.
> You might have noticed several unusual things about how I discuss Autism. I’ve capitalized Autism, and I have not once used the word “disorder” or “syndrome” in tandem with it. I also say Autistic, rather than “person with autism” -- the term Autism Speaks, an organization despised by most Autistics and many of their parents, would prefer you to use.
Also, it's a lot easier to just use 'they' instead of he/she most of the time anyways, food for thought.
The author appears to prefer the term Autistic, and has specific reasons for disliking Autism Speaks (and the term "people with autism", with the author claims is promoted by Autism Speaks), as described in [0] and [1].
[0] http://www.stanforddaily.com/2014/05/27/autism-allyship-and-... [1] http://apoststructuralautistic.wordpress.com/2014/06/19/my-a...
A parallel issue is expressly the case here -- as is mentioned in the article here.
(Even if you are in the group to which the alternative labels would apply, its not a great idea to pretend that your preferred label is the preferred label of everyone in the group.)