I was picking up two passengers. I arrived and got the passengers in the airplane. I see a lot of the same passengers every day, but I had never flown these people before. One of the passengers was riding in the front seat next to me which is allowed under the regulations for our type of operation and aircraft. I knew that they had flown with another company pilot earlier in the day, so I gave an abbreviated passenger briefing including seat belts, flotation devices, emergency exits, and what to do in case of an emergency. I did not include crew-member interference in the briefing, and that turned out to be a mistake. We departed. It was a nice day, and there were quite a few other airplanes out flying. The passenger in the front seat kept pointing them out to me. I didn't really mind him doing that then because we were in cruise and it's alright to have two sets of eyes looking out for traffic, especially during low workload times. Then he noticed the analog cylinder head gauge wasn't reading any temperature, and he began to tap on it. He kept tapping at it then looking at me, so I felt compelled to talk to him. He wasn't wearing a headset so I yelled over at him that we have a digital cylinder head temperature gauge, which I pointed out, and I told him that everything was fine. As we began to descend, I was getting busier. He pointed out another airplane that I was in radio contact with. The passenger pointing out airplanes was beginning to get distracting, so I nodded at him and motioned for him to put his arm down.

He was monitoring my descent profile very closely and scanning the gauges. I thought that maybe he was just a very keen passenger, but had a sneaking suspicion that he might be a pilot. As we got on final approach, he jerked his arm up violently to point out what I was sure would be an airplane that was going to hit us. It was a bird which was about 100 feet above us. However, his action startled me, and I was beginning to get angry about his over-reactions to everything. At this point we were short final, and I was fighting a little with a gusty cross wind. Just after touching down, I felt an incessant poking on my throttle hand. I was attempting to ignore it and focus on directional control, but eventually looked down briefly during the roll-out. Of course, the passenger had been poking me in the hand, and then once he saw I was looking, started pointing and tapping on the prop control which I had left in the cruise position and had forgotten to push forward. I quickly ushered his hand away from the engine controls. Now I was sure he was a pilot, but as I was taxiing off the runway I was seeing red I was so angry. I glanced over at him for a second and he looked very smug that he had gotten to correct a perceived mistake, which of course made me angrier. I simply could not believe that a possible pilot would have interfered with my duties during a critical phase of flight for something that was no longer relevant, especially after having startled me during the final approach anyway.

Once we were parked, I asked him if he was a pilot, and I discovered that he was a private pilot. I did discuss with him my crew-member duties, the various distractions that he had caused me during my duties, and how to not interfere with a crew-member again.