Type 1: The mom with a special-needs kid.
Type 2: The mom with a typically-developing kid who notices that you have a special-needs child and either acts normally and/or tries to get her child to engage with yours.
Type 3: The mom who notices that your child is a special-needs kid and when your child tries to interact with hers, she suddenly hovers nervously and/or whisks her precious little one away.

Does he look like a menace to society?
Mostly, I've met Type 2 moms but the other day I encountered a Type 3 at Borders. Max was running around the kids' book department; another little boy overheard me saying "Max, please come here!" and asked his mother "Who's Max?" When Max came over I told him "Go on, say hello" and he parked himself in front of this child and said "Hi!" Which is awesome, we love when Max articulates a "hi" to anyone. The little boy said "Hello" back, and then Max just stood there and smiled, and drooled a bit, and reached over and patted him on the head. That is when it dawned on the mother that Max is a special-needs kid, at which point she said "OK, Sam! Let's keep looking at books!" and sort of hustled him away. You know, I'd understand if Max had hit this kid or shoved him; I would pull Max or Sabrina away from any kid that did that. Except Max didn't. He was just being friendly.
This sort of thing used to make feel bad. But now I think "Too bad her kid is missing out on meeting Max." And "Too bad her kid's not going to grow up understanding that there are all kinds of people in this world." And, "Dumb-ass."