All calls of this nature will be purely subjective, as no criteria has really been set. It's kind of like the "strike zone" for baseball umpires...some have different degrees of tolerance and it's up to the hitters and catchers to understand those tolerances before they go into the game.
As this newly "tightened" rule gets enforced, players, coaches, and officials alike will get familiar with eachother and eventually it will normalize. Of course there will still be biases (human nature) against guys like Rasheed Wallace, Ron Artest, etc.