The definition of "combatant" is a completely different one than of "armed".

I agree with Seabee on the "taser" example.

@Wilf:
International treaties gain the power of law with ratification, so it's not inappropriate to call GC III and IV the laws of war.

@Uboat509:
American forces have stretched claims of "self defence " so far that I've become allergic to this excuse.
Think of Mach 2 fighter pilots bombing wedding festivities in response to AK muzzle flashes, claiming to have acted in "self defence".

There was no line of sight between ground forces and the suspected RPG at the time when the AH opened fire, so there was no self defence at all. Self defence ceases to be possible once the aggression is over.
Here wasn't even an aggression.