Yes, some really dumb **** goes unpunished, but the players know exactly where the line is. Go to the ground, get flagged. Use a prop, get flagged. Dunk the ball or jump in the stands, no flag. Run to the center of the field, no flag. Taunt in someone's face, flag. It's very simple even if the rules and exceptions are stupid. Kind of like in-the-crease. It was a monumentally stupid rule, but it was the !@#$ing rule and should have been called.
Sometimes guys will get away with doing stuff that should be flagged (though rarely are those the guys with a history of doing it). But you never see a guy get flagged for dunking or leaping. That's the point. They know what's legal and they do that instead of something that isn't.