My son is 3 1/2 yrs. w/ high functioning Autism. How I respond to others really depends on the situation.
Some folks here may remember a rant I went awhile back w/ a RUDE lady at a grocery store. She basically accused me of bad parenting and I kinda went off on her about Autism and invisble disabilities and how people should think before they speak.
Usually if anyone makes a comment I just say "He's autistic." And leave it at that. I don't go 'round wearing a t-shirt that says "My kids Autistic" but I don't hide it.
If someone makes an ignorant comment I use it, usually, as an oppurtunity to educate them about ASD and related disorders.
If someone is especially rude I USUALLY ignore them.
I don't just casually bandy about my sons issues unless there's a reason to.
Like when we were on vacation a week or so ago. At the hotel room my son decided to have a grade A-1 meltdown. I kept waiting for someone to come to my room thinking I was abusing my kid!
The next morning I went to get some donuts and coffeefrom the "continental b-fast" and my next door neighbor, as t'were, was also coming out.
She asked if my kid was ok, and I said "yeah, just a tantrum." She said "Some tantrum, that childs got a future as PE Coach with yells like that!" I just laughed and left it at that.
Sara