If you want to make enemies, try to change something.
When societies rules fail ...
There was a system like this in the early days of FOnline. The more players someone had killed, the worse their karma. The worse their karma, the darker red their nickname. It was incredibly simple and probably a bit misleading in some cases, but it worked. You had a rough idea of who to avoid.
i'd say 3.5 hours since the last PK, mindless PKs are like pixel junkies, they want to see little red hued pixels slosh around on the screen.