Eh... people are ignorant about disabled people really. Anything that upsets their perfect world view should not be put in front of them. (Some people really think that way I think.) I get people glaring at me all the time and comments about 'not controlling your son' when he gets a little upset or overly playful when in public. I really really try to stay unaffected and not get mad at them.
Many times I just smile and say "He's autistic. Would you like to ask any questions so you understand better?"