Priests should be one of the easiest characters to have fun with. Just start a religious war. Pick a likely religion that your members already don't like, if you can. Or pick one that is prominent in an enemy realm. Find a way to vilify it. Start badmouthing their realm in your regions. Maybe, when no one is looking, start a religious riot against them. Get a sympathetic lord to burn a temple or something. It may take some time, but if your realm is otherwise boring with no wars/conflicts, this may bring people out of their shells and get something started.