Good point Schmeck about the "food for thought..." We always want to protect our children or others we identify with. I try very hard not to say something mean or even directed at the other person, but more "educating" about the situation at hand.
I have had kids with autism do things that are not acceptable, even by "spectrum standards' (that is, i may not pay attention to a kid who wants to feel the texture of my tires, but I will say something to the parent if the kid hits or grabs me). I just ask the child (and parent within hearing distance) to stop what they are doing, that it is not nice/that it hurts/that is it not ok.
When someone says something rude about a person, and no one was injured or could have been injured in the incident, it is really hard not to tell the person off.
My preferred method of dealing with rude people who should know better (I put people above age 12 in this category) is to educate them as to why they are ignorant bigots (obviously without using those words), using words as if I was speaking to a 5 year old. Basically I say politely and without sarcasm or condescension something to the effect of "He is autistic and epileptic, so he uses this as a wheelchair. We call this a special needs stroller. See how it is made for a bigger kid. This lets us take care of kids who do not or cannot use a wheelchair like mine."
I would say this to a kid who asked a question - I get questions from kids all the time about my wheelchair and I am happy to answer. Kids are not asking out of pity or cruelty - they actually want to learn. Adults, who can read all about wheelchairs and everything on the internet, are a different story.
I have discovered that adults do not like being spoken to like a child, but as long as I do not "talk down to them" (like using a higher pitched voice like when you talk to a baby) or be sarcastic, there is very little they can do about it.
Here is something that happened to me in DL last week. I was in the smaller of the two disabled stalls in the restroom. A woman with a
scooter was in the bigger one. As she was trying to back her scooter out, a family with a stroller was in her way, would not move, complained about how long it took her to get out of the stall, etc. The woman in the scooter said something to the effect of "You are making it very hard for me to get out. And using this stall just to change clothes with the stroller makes it hard for people with disabilities. These stalls are for disabilities."
The woman with the kid/stroller just said "yeah, whatever." And then began helping her daughter change out of her Jasmine outfit - not even a potty break, but a changing room!!!
I said from the next stall over "It is not "whatever" to those of us in wheelchair or with other disabilities. It means we have to wait much longer when regular stalls are open. So it is not "whatever" for us to sit out there waiting and pee our pants because you like to bring the stroller in with you."
The woman did not reply in English, but I know enough Spanish to know she called me very non-Disney names. What I said is true, and I did not speak down or in an angry voice. I just said it like we were having a conversation...
It is hard to call people out, because I cannot tell if they have a disability just by looking. I was responding to what she said. But there are times even I have assumed that a person did not need to be in the handicapped stall, based on two pairs of feet, and the kid seemed big enough to go on their own. Then a woman and a girl with Down Syndrome walked out. SO glad I did not say anything!