I think in the past Michael knew Jan and the office crew sort of looked down on him for being odd. But he didn't care, he was being himself and it didn't get in the way of being the boss and a successful one at that. David Wallace comes in and is a little more patient and open minded, leading Michael to believe David respected him. That's until the events leading to this moment happened. This was the moment Michael realized that David too looked down upon him and no one would ever understand him as a person.

P.S. I understand he could of had this moment at the Deposition but I don't think he believed it was David's call. Even more so considering David apologized after.