The difference between APK and PK lies in shooting bluesuits/low stuff/low level players.
In fact, since so many people get caught up in this apk/pk thing (hurr durr you are Anti Player Killer but you killed a player in tc so you are not Anti PK anymore durr) it's better to define it as Bluesuit Killers and Anti-Bluesuit Killers.
I'm aware that me and my statement will get trolled and flamed to death but the point is that todays' APK only kill people that are either known enemies or that look like trouble (eg an unknown player with metal armor and big gun on reno). It still lies in every players' hands if you spawn to kill that guy in metal armor or not, different gangs have different attitudes there.
What all APK gangs have in common is that they don't initiate a fight and don't go against players they don't know who are in lower gear/lower level.
And above all that, the law of the wasteland still stands. If you encounter a known APK guy, you don't have the "right" not to get shot to rely on. The wasteland is no constitutional state. However, in Redding you at least have the chance to get justice.
In other words, for the guy that has been playing for 2 weeks, hanging around ncr and crafting shotguns, APK and PK matters.
For everyone else who posts in this thread, it usually doesn't and it's just used a troll argument.