That armor doesn’t mean much when a muzzle flash comes your way. While Batboy apparently had a helmet on he was wearing a gas mask on his mush. His head is the target, especially since his lower body was mostly screened by chairs. Any reasonably competent shooter can keep his rounds on a head sized target. When trying to take a dumbass out of a fight one does not aim for a non-lethal spot. Besides any bullet with 300 or more ft-lbs of muzzle energy will most likely knock the dummy off his feet, even if armor stops the round, long enough to subdue him. Picture this: 300 ft-lbs of muzzle energy is like getting hit by a linebacker full tilt boogy. 9mm or 38 spl ought to do nicely. No doubt in my mind just one armed citizen could have done a lot of good. Remember the one chick who unloaded on Hasan at Ft. Hood and “secured his operation”?
For every action there is an equal and opposite reaction.
When you pull that trigger that bullet has as much force as the recoil in your direction.
If it was like a linebacker full tilt, you would be on your ass every time you fired a round.