The thing is, my character didn't have a set static response to everything...
I do my best not to metagame
You asked us not to comment on the incident, but rather your role playing. I will respect your request, but ask that you not keep bringing up specific circumstances of the event to justify yourself, as that makes it hard to avoid responding to.
Your character may not have had a static response to everything, but he did have a static response to the circumstance "someone is doing something I don't like." There are multiple variables that you did not take into account, such as your character's lack of social skills, meaning he had no idea whether the negotiation was going poorly. But you, the player, did and you gave your character that information. That is meta-gaming.
You also didn't factor in your own character's inexperience in the shadows, the other team member's reactions or the fact the face had a noticeable, tangible affect on the mood of everyone around him.
All of these circumstances are something your character would have considered, but you dismissed them.
That is not playing a character, that is playing an action and using certain surrounding circumstances to justify that action. But just as you hand waved off the circumstances I listed, and others I'm sure, you could have waved off the ones that led you to your course of action.
Your character considers all circumstances of his environment as that is the only world in which he lives. You and I have the misfortune of living in both, and often times more, worlds and so cannot let your outside prejudices and judgments in.
More important than any of this, however, is the idea that you cannot judge your character. Well you can, but it doesn't lead to good role playing. Your character is neither good nor evil nor indifferent. He simply is. He exists as fully and wholly and deeply as you do.
You have judged your character to be a curmudgeon. Who determined he is a curmudgeon? If it was you, then you have to get away from labeling your characters with such broad strokes. Answer, instead, what he does that might make others consider him a curmudgeon. Does he interrupt people, complain, make snide comments, etc. Are there circumstances in which he would not perform those actions, such as letting a little boy inside his floating house so the boy doesn't fall off and die?
And who is it that considers him a curmudgeon? Surely not everyone in his life. How do those people see him? Why can they see him differently than others? What playable actions does he perform for those people that he doesn't for others and what goal is he trying to accomplish when he does? What goal is he trying to accomplish when he acts like a curmudgeon?
When you judge your character, you distance yourself from him. You play him, not as a character, but as that judgment. You judged your character to be a curmudgeon and, thus, when presented with a circumstance you did what your idea of a curmudgeon would do, rather than what your character would do. A judgment doesn't have to live in the world. It has no bills, friendships, history or goals, thus it has no care for the results of it's actions. A character who acts curmudgeonly does, thus he considers all circumstances of his environment.
Unless he's drunk. It's hard to play drunk.