Obviously this man has some VERY serious issues. You were probably right to just not go but I think I would have gone just to spite him. (show's my immaturity right?
) Did you check with any of the other parents to see if anyone else felt this way? This was most probably just him on some sort of crazy power trip. It's not his kids fault, but I definitely wouldn't be fostering any friendships between your DS and the other child. (although it would be kind of funny if they became best friends and then the dad had to eat his words)
I'm so sorry he put you through this and good luck if you ever run into him at school!
