I suppose for most people, looking "autistic" basically means you are ret*d by most social standards. You can't dress yourself, you yell and scream randomly, and basically you're a vegetable. However, most of us with a high functioning form of autism, or Asperger's may look and sound completely normal.
For me, I look like any normal teenager, but when it comes to my voice and facial expressions I'm pretty different. I've got the classic monotonous voice and the straight face, along with the refusal to make eye contact. But other than that, I know I look relatively normal.