We have this line of personalities, ten in all
http://wiki.guildwars2.com/wiki/Personality
They are easy to tweak, just talk to a speed-booster in any city until you get the personality you want.
Right now they have no effect on anything other than NPC dialogue choices.
It’d be cool if personality actually had some use in-game.
One way this can be done, is with allied buff-priority.
Right now, AoE buffs affect party members first – this could be expanded to prioritise matching personality types second.
For most people, personality will still mean very little.
It’d have significance for members of groups larger than a party (eg a guild); they could all tailor their personalities so that they’d be more likely to receive friendly boons.