Don't you think a little perspective is called for at times? You're saying that someone who doesn't park correctly between the designated lines would be enough to piss you off to the point of keying that persons' car? I have to say that if I were a third party witness to something like that, it sure wouldn't be the person with the deficient parking skills that I would be reporting to security...or the police.
Just remember, as you are being ever watchful for opportunities to point out other people's mistakes, there's a good chance that someone is watching you too.