I would argue that he is selfish and inconsiderate.
He is refusing to speak to a person because they have made policy changes he doesn't like, which shows that he is inconsiderate of another person's feelings. In addition, he does something purposefully just because he feels like it, without regard for the rules which is incredibly selfish. Not following the rules to help yourself out with the possibility of it causing harm to others, is a big sign of a person being selfish and inconsiderate.
You might say he is immature, but there isn't much in the text to support that he is grumpy, although that could be inferred.
