Please don't undermine me in my own car!

I was driving happily southbound on Yonge when I pulled into the turning lane to make a left on a side street just south of Steeles. There was a line of cars heading northbound that was stopped, waiting for the red light to change. As always, there were rude/incompetent drivers who blocked off the intersection. As luck would have it, there were a few people who stopped just short of the intersection to give me room to make my turn. Grateful for their consideration, I gave the courtesy wave. Everything was fine until Steve, who was in the passenger seat, gave his own courtesy wave.

This was not the first time he's waved along with me. This was also not the first time I've yelled at him for doing it. I felt that his wave undermined mine, as though he felt that he had better give the wave in case I don't for fear of appearing ungrateful. I have always given the wave and he's seen it on many occassions so my willingness to give it was not in question. Where's the trust? His excuse was that he was thankful too and wanted to give the wave for himself, rather than on my behalf. I argued that one wave is plenty to show appreciation and asked that he stop giving anymore in my car.

This may be worse than having my passengers shoulder-check when I change lanes. AARRGGHH!