Continuing the thoughts from my last Felltower post:
What traits in GURPS are generally those that would mark a being as generally hostile?
This is largely from a fantasy or space opera perspective, and includes some things from GURPS Dungeon Fantasy . . . but much it applies in general. If you have an addiction to murder and a sadistic streak, you're probably a monster in any game.
These traits are ones that make it more difficult to get along with a given being. They're not pleasant, but not necessarily monster-like or capital-E evil.
Good examples of these are Bully, Bloodlust, Callous, Intolerance, Sadism - these all make it more likely than not you'll earn a hostile reaction eventually.
Paranoia and Megalomania - eventually these will put you at odds with others, either through your fear of them or your assumption of superiority over them and your attempts to asset it.
Bad Temper, Berserk*, Compulsive Behavior (Fighting) - these all make it likely you'll eventually provoke a response by your actions - you'll take direct action that leads to violence, resort to violence, or resort to some kind of insult and end up fighting.
Social Stigma (Outlaw), Social Stigma (Excommunicated) - these classify you as an "other" due to legal or religious reasons. You'll get treated poorly by society and by individuals within that society - Social Stigma (Outsider) will do the same. If you couple these with one or more of the above, especially the ones just above, you'll eventually end up with bad problems. Expect such combinations to spiral - especially the usual Bad Temper/Bloodlust/Overconfidence trio on top of any of these.
Fanaticism - especially if to something evil or hostile.
These traits generally make it impossible for you to get along with others in general. It's likely if you have one or more of these, you're likely to considered a "monster" and killed out of hand.
Compulsive Killing, Odious Personal Habit (Eats Other Sentients), Uncontrollable Appetite (Mortal Flesh) - these kinds of traits make it extremely hard for anyone to treat you as much except a monster. This is double true if combined with some of the traits above. Add Bestial if you really want nothing and no one to like you at all.
IQ 0 or close to it, combined with any traits that make you regard other beings as food = likely monstrous in society's eyes. No one one likes to be eaten.
Social Stigma (Monster) is one that's not your fault in and of itself; it's possible to have this and no other negative traits. It's more likely, though, that this is just society reacting to the actions of your race. This isn't one you'd commonly expect to find on its own.
These aren't actually disadvantages, but they are traits that define you.
Truly Evil. This is just a 0-point entry in the Notes section of a monster description. It doesn't really require a trait - you could have nothing but positive traits but be otherwise allied to Evil, and affected by spells that have some sort of special effect on Evil. You may not be a "monster" by any other definition, but you're one of the bad ones.
Unwilling to negotiate. This knocks off your other option for dealing with such beings. If you or they have this, it doesn't really matter if one of you considers the other a monster or food or whatever. Your common ground is fight, or flee.
- I'm sure I'm missing some obvious examples of traits that point to unpleasant or monstrous behavior. Let me know in the comments, and if I agree, I'll add them.
- I left Greed off on purpose. It's not a positive trait, but I don't see it directly tied to behavior that leads to violence, or gets you treated as a monster or close to it. It's not a good one in combination with others, but it's not quite as chilling as Callous or Fanaticism or Sadism is, in my experience.
* I've occasionally told players that taking Berserk on a character is a) a disadvantage, and b) will eventually lead to your character's death in combat. They still take it, and they're still disappointed when they die in combat.