The bottom line is this is more than just irritating. He is having a negative impact on the safety of the flight by not allowing you to do the job you were trained to do. There is no doubt he is not good enough to do your job and his, but that is what he is trying to do. Calmly and assertively tell him, "Look, I know you think you are helping me but you are not. Your comments are a major distraction and keeping me from performing the job as I was trained. Unless it is an immediate safety issue, let me fly, and if you feel the need, critique me AFTER we are parked at the gate." Do your best to fly by the book and the way you were trained. Remind him of this and tell him if he has a problem with that, take it up with your training department.