Its not that out of character for Riker, he has a habit of sulking when things don't go his way. Look at his reaction to Troi's potential marriage or his treatment of Shelby and of Ro, and in the Outcast he ignore the prime directive and goes on an unofficial rescue mission.
If you watch Frakes performance he has a habit of looking irritated with people very quickly, often with very little reason.
As to the insubordination, once the mission was over I suspect that Jellico was happy to let the matter drop. notice that Riker is in uniform on the bridge when Picard resumes command which Jellico did not have to allow ( In fact given that Picard presumably needed a couple of days to recover from his ordeal and that Data is at Ops he may even have reinstated Riker as first officer).