Posting here so you can all give me a good slap and tell me not to be such an arse if I am BU.
DD, DP and I were at barbie at weekend with his two DD's. Lots of other parents with their DC. First I saw this boy is when DD was playing with a toy house. He kept running his car all over it. DD asked him to stop but he just ignored her and carried on. It wasn't her toy and I took the view that she should really share it as there was lots of kids there, but she wasn't having any of it.
I asked the boy, who was about 6 or 7, if he would play round the house instead of all over it but he just looked right through me. DD was getting really upset and trying to physically move his hand away but he was just carrying on. DD can be a bit funny about sharing so I didn't want to make a scene but had no clue what to do beyond taking the toy away. Fortunately at that point the boy's father came over and called him away, saying that he shouldn't be playing with doll's houses 
Later DP's DD came over and told me about this rude boy who had pushed her off a swing and said "Are you blind"? when walking behind her. I asked what he looked like and she described someone similar to this boy but as there were others who fitted the description I didn't want to jump to conclusions.
Next incident I witnessed was the boy trying to get under the table where some of the girls had made a den. He ignored their requests to go away until they were literally screaming at him, and still seemed unfazed. He seemed to have no concept of personal space and it appeared their distress left him completely unmoved. Again some parents had to intervene.
Final thing I witnessed was outside. He was trying to grab a bag of sweets from this girl who was carrying it. Again he ignored her telling him to leave her alone. He grabbed at the bag and she tried to push him away. He then hit her on the cheek. I shouted at him to stop. He just stood there with a faint smirk on his face. Completely unmoved. At that point his Dad came out and I told him what happened. The Dad was suprised and shocked. The boy only said, quite calmly "It wasn't on the face" The Dad then asked the girls what happened and they told him the same. At that point the Dad took the boy to his car to give him (I presume) a good talking to.
While they were there I asked the girl was ok. She was fine - I was more upset than her I think!
They got out of the car at the same time we were leaving, and DP's DD said "That's the boy that was horrible to us"
So what I want to know is, am I BU/small-minded/naive in being freaked out by his behaviour? I'm around kids a lot and nothing much fazes me. Quite a few kids I know have SEN or ASD traits and I never automatically assume a kid is being "naughty", esp if they're distressed. But the way this child just stood calmly in the midst of all the chaos he was creating was quite unnerving.