Maybe I'm just getting old, but I don't have much of a problem with that Video. The Cop did over-react, but then, 90% of being a cop is having respect, for every cop, there are tens of thousands of citizens.
The kid was being stupid, the cop doesn't want a confrontation, he just wants to get back to his job and hopefully not see anything too unpleasant before he goes home that evening. What he does not want is to be given lip in front of members of the public by a kid trying to impress his mates. That would have got him a clip round the ear 20 years ago, and really should do the same now.
So, yeah, they caught the cop on a bad day, but all young animals naturally challenge authority, and authority naturally smacks them round the back of the head, it's part of the great cycle of life.