Buffy fans might be pleased to know that Nevada self-defense law and Washington self-defense law state that homicide is “justifiable when committed” “[i]n the lawful defense of the slayer.” Well, all state laws say that in essence, but Nevada and Washington actually use the word “slayer.”
Those with a taste for the vivid might also consider the word “manslaughterer,” which is not mentioned in any American statutes but does appear in 10 cases (according to Westlaw).