People that are evil and vicious just can't hide for very long. Underneath the charismatic façade the narc displays to the world can be an easily angered sadist. Sadistic acts are their way to punish those who are not being compliant, admiring or indulgent.
Know this, my beloved brothers: let every person be quick to hear, slow to speak, slow to anger; for the anger of man does not produce the righteousness of God. ~ James 1:19-20