who determines what is appropriate treatment of someone based on who they are?

I believe Adam Smith gives a good explanation of propriety (appropriate behavior) in the Theory of Moral Sentiments.

"When the original passions of the person principally concerned are in perfect concord with the sympathetic emotions of the spectator, they necessarily appear to this last just and proper, and suitable to their objects; "

Smith is saying that our behavior is appropriate it is in concord with what is expected of us by others. It is expected that a student listens when a teacher is talking. It is expected that you hold the door open when someone is coming behind you. It is expected that you don't chew with your mouth open. When we are meeting these expectations, we are in harmony with everyone else, and we are acting appropriately. When we began to not act appropriately, we become out of sync with the rest of society.

Let's assume that the student believes they are treating their teacher appropriately when they talk in class.

What's proper is decided by society, not by what an individual believes. I'm not saying that what is appropriate is always right.

Certainly, self-aggrandizement would not be problematic if it were honest, but it is very difficult to determine whether said teacher truly is that important.

If you want to act appropriately, you behave in accordance to what is socially expected, to the best of your ability of course. But I don't see how it is demeaning that society has certain expectations for your behavior.

Perhaps the student has observed that he learns nothing in that class because the teacher is bad. Is this teacher not less important than if the student actually learns something from him/her, and would the teacher's sense of self-importance not be misplaced? Is paying attention to a poor teacher really more important than socializing with friends?

The student should have enough humility to realize that while he might not enjoy the teacher, his peers might think the teacher is teaching well.

The teachers importance is automatically given when he/she becomes a teacher. If the teacher is not doing a good job, than his/her overseers can take care of it. The student is in no place to be making decisions on whether a certain teacher is qualified or not.