Second, I did not "pull a switcheroo." I was consistent in this sense of the dictionary definition of subjective:
3 a : characteristic of or belonging to reality as perceived rather than as independent of mind.
At issue here is DC's statement that he is justified in initiating force if he perceives himself to be in danger. There is no room in this for the gunman's actual intent, or any actual threat -- DC's justification for shooting is based solely on his perception of the gunman's intentions.
The justification for violating the non-initiation principle is therefore explicitly subjective.
leading to the absurd conclusion that to have a limited or incorrect perception of specific facts is equivalent to being disconnected from reality and guided by arbitrary notions out of one's head.
It's an "absurd conclusion" only because you've added an absurd statement that I did not make. Nobody but you said anything about the threat being arbitrary or disconnected from reality.
OTOH, the threat may seem very real, and yet not be a threat at all. For example, cops sometimes mistake the motion of reaching for (say) a wallet, as a move toward a gun; or the pointing of a plastic toy gun as the pointing of a real gun. In such cases we might excuse a mistaken shooting on the basis of "reasonable cause."
The simple fact is that a subjective assessment ("I believe I am being threatened") is deemed sufficient to overrule the supposedly absolute non-initiation principle. As such, there is indeed something "relative" about it.
If you can't see that the "initiation" starts when you POINT the firearm or advance on someone with a blade or cudgel, then there is no further point in talking to you at all.
Your "consistent" definition is irrelevant. In the context of philosophical discussion, the distinction between "objective" and "subjective" is not merely the difference between reality as it actually is and reality as we are best able to apprehend it through our finite senses and knowledge -- it is, instead, the more fundamental difference between a fixed universe "out there" and a malleable universe inside your head. By invoking the former and implying the latter, you are (as a matter of objective fact) pulling a clintonesque switcheroo.