Someone has to do it. That's why police officer positions are one of the best jobs for job security. And they keep getting raises every few years as well. I've been on several ride alongs with some cop buddies of mine and let me tell you.....it's a stressful occupation where jerkoffs are constantly lying to you and your actions are always under a microscope. You think that's an example of abusing your power and authority? Ridiculous. The people getting arrested are the ones with all the rights.
That kid was acting like a smart-aleck jerkoff and he initiated movement towards the officer. The officer has no idea if the kid is possibly armed or dangerous and he was in full defense mode.
Now if the cop would have stretched the kid's underwear above his head in the form of an atomic-wedgie....well, that would be crossing the line. Give the officer some credit for showing some form of restraint in that department. 
I don't give him any credit.
This asshole deserves to be punished for his abuse of power.
If the cop was really afraid some scrawny punk running his mouth was going to pull a weapon and blow him away,
then all he had to do was restrain him.
We don't know if the cop was saying something to provoke the kid to run his mouth either.
I've watched the show cops; these high and mighty police just love to hear themselves talk from their moral high horse.
As upinthemguts said, this sort of behavior leads to police shooting people dead because someone moved the wrong way.
The police should fear being reprimanded for using force; for our own safety.
Whether you like the punk kid or not, this could happen to anyone.
What I see in the video is an asshole trying to impress the female cop by picking on some scrawny guy.
Typical neandertal behavior.