I agree with syoblrig, this is not a common or normal reaction. My DS has always been similarly conspicuous, but we've never encountered any such reaction. (Clumsy reactions, yes; malicious, no.) Don't let this colour your expectations. I hope you never encounter anyone else who behaves like this!
I disagree. Though this behavior is unacceptable, under certain conditions this reaction is both common and normal. The necessary conditions are where a parent overly identifies with their child, seeking value and validation through them. "My children are super-awesome, therefore, I am super-awesome!" We've all met people like that. A child who stands out from this person's children in some way is seen as a threat to their own self-image.
In other words, the adult is making it all about themselves, and not about the children. This is a common refrain when children are being victimized by adults in some way.
These parents are usually the hyper-involved parents, too, because they're so busy building up their children in an effort to build themselves up. So they're frequently the soccer coach, the troop leader, the PTA president, and yes, the community center volunteer.
