I think the relationship status probably trumps traits as far as what default interaction will happen first.
Take Geoffrey Landgraab for example. He's a charismatic sim with a good sense of humor, which generally means this sim will be friendly to just about anyone. Yet if he runs into Nick or Vita Alto on a public lot, more likely than not, his first response will be to react to the presence of an enemy sim, and do that "no" symbol thought bubble over that sim's face and an angry animation.
This is also compounded by how the game remembers whether the last interaction a sim had with someone was positive or negative, and it affects the decay of a relationship. (I remember reading that in the Prima guide, anyway.) So if the last thing that happened between the sims was negative, it might create a higher chance for their next interaction to also be negative.