How to deal with peoples' ignorance and rude comments?

I have asked a question similar to this; about my son and bullying. But my fiance has Pervasive Developmental Disorder (Pretty sure that's the name of it) and he's 26 and acts about 15. I love him to pieces and I think he's the sweetest guy ever; some things about him are normal for the age but some you wonder if he's younger. He's pretty normal until you talk about something he's immature about. He's a great "dad" to Roman, my "son" who's a family member we took in, but a lot of people are really rude about him and make comments to me. He is able to hold a job; he works at Kohl's. I work at a summer camp and some of the other staff make comments about him to me, I've had the same problem with parents at Roman's school. Can someone give me advice about what to do about people targeting Kamil? I hate when people are so shallow, he has a disability. And no sarcastic answers, please and thank you :) - Macca