It such a dumb idea that it is discussed at length in every self-defense class I have ever taken.
Throwing something in someone's face is the crime of assault. Throw popcorn in a cop's face and see if you go to jail.
Showing a deadly weapon without the justification to use it is a crime. Walk up to a cop with a gun in your hand and see if survive long enough to go to jail.
If it was not reasonable to shoot the popcorn thrower, then it would not have been reasonable to display a deadly weapon.
If the cop had brandished his weapon, would the popcorn thrower have been justified in drawing a gun, assuming he had one, and firing? If the ex-cop had ended up dead in that way, would you then be calling for conviction of the popcorn thrower for murder?
Whether throwing popcorn constitutes assault is one question. Whether that rises to justification for lethal response is another. There are degrees of assault, and I imagine that throwing popcorn falls in the lowest level of assault. A level of assault where the target should have no valid, let alone sane, reason to think their safety was in jeopardy.
Seriously, you are harming CCW with this kind of nonsense. Sometimes (and rarely) the CCW holder is just plain wrong. From all I have seen so far, this is one of those cases.