Ya know, when my BCI had mites, she was pretty cranky. She hissed a struck at me one day. Perhaps somthing is bothering Rex? How is your temps/humidity? Is there a possability that he has mites or internal parasites? If everything husbandry wise and health wise is ok, id say you just have a cranky one on your hands that needs to be handled alot. He will eventually calm down.
Good luck with that