Well, while it's obnoxious of other parents to comment on it, I think that the truth is that he is somewhat "difficult" for other people, from your description.
My probable response to that kind of statement from other parents depends on who is saying it and the other circumstances (yes, pretty invasive/intrusive, but hey... you wouldn't BELIEVE the hurtful garbage that I have heard...):
a) the stare. If you can muster a look of mild disapproval mixed with amazement that's even better. Say nothing-- because you are just as speechless as if the person had just mentioned that they encourage their dog to defecate on your lawn. There are things that civilized people pretend to not notice-- at least to SAY, anyway-- and this is one of them. Would they also say "Wow, you must struggle with a child so obviously uncoordinated."? Probably not.
b) The question (but you MUST keep your tone perfectly neutral, maybe even a little pleasant): ~awkward pause~ " What do you mean, 'difficult?'"
The bottom line is that it is NONE of their business, and you probably cannot 'educate' someone about it to any useful effect, so discussion is a waste of time. And it annoys the pig, by the way. While one-upping may feel gratifying in the moment, this is modeling the exact same sort of retaliatory behavior that you do NOT want your son using, n'est pas?
If you have no idea what is behind your son's behavior, and it seems to be global, it may be a developmental thing for him. It's possible that he's just struggling with who he is, and where (metaphorically) he is headed, and how he's going to fit in. Unfortunately for you, it sounds like you also don't have any kind of roadmap for understanding his motivations/intentions/feelings from the inside out. That is very frustrating as a parent, because it leaves us powerless to do anything to HELP our children to develop healthier communication and coping. A professional can be a good resource if the problems are having a really significant impact on him.
Does anyone else in his family have experience from that perspective? Usually such character traits (if that is what they are) will be present in at least a few relatives. They might be able to offer some clues for you, and perhaps a different way of viewing the behavior. That could lead you to some ways of channeling it or modulating it without changing WHO your child is. That may be a better strategy, if this is a hardwired trait where you and your child differ significantly in character, personality, or temperment.
