When a Virtue reaches zero, the character must immediately roll Humanity, difficulty 8. No more Humanity can be lost for sins against a zero-Virtue, but neither can it be used to resist Frenzies. Courage can be substitututed for one of these Virtues if that trait is higher. Some characters have a personal moral code which justifies certain actions. Examples might include Assamites, for whom contractual murder is legitimised in the service of the Clan, or Ravnos, whose culture condones robbery and fraud.
Any character can have scruples so long as they fit in with the character's concept.
Some vampires reject their Humanity and practise the inhuman virtues of Callousness and Instincts. To follow these Virtues requires the character to study one of the Paths of Enlightenment. Callousness and Instincts are used for Degeneration checks just like Conscience and Self-Control. These sins involve pitying or respecting human beings and denying your vampiric needs for their sake. This generally involves treating mortals as anything other than food.