How do would you deal with a disrespectful kid?

I just finished witnessing a 6 year old (who is too smart for his own good, really), whom while being reprimanded by his father for being defiant when dealing adults and cruel to his playmates, have a rather subtle smirk on his face. The boy was told by his father to get rid of the smirk, but, he continued.. I just stood there and couldn’t believe it. I may sound old ;-), but back in my day, you would never disrespect your parents like that.. Yikes.

Also, there’s nothing worse than a bratty child? Wouldn’t you agree?