Eh, I dislike ignorance...in myself. In other people, I tend to view it as an opportunity to talk with them. Which may not always be a good thing. Same for feeling stupid - it doesn't help. Though I have learned that making fun of my experiences is something people like.
Though when other people feel stupid around me, sometimes that's not good and I need to encourage them. No one is truly stupid all of the time and about all things.
I have made my peace with subjectivity by stating that there are some things that are true of other people that aren't true of me. Not true for other people, but true of them. Therefore, all things are objective. For example, "Sam thinks this is true" or "Sam has this experience and therefore interprets what Dan is saying to mean this thing" are both objectively true statements about Sam and Dan.
This allocates for the fact that all of us have different viewpoints - I mean, if I'm sitting somewhere in a room and you're sitting in a different spot in the same room, you're going to have a slightly different view of the room - that's a function of the physical location of your eyeballs. Likewise, the amount and types of information in your head is a function of your life experiences and education and your relationships, and the information in your head causes you to process new information differently.
So yeah, if you use subjectivity to mean "relativistic truth" than you're wrong and I will be giving you a lecture, but if you're using it to explain different perception of the truth, I'm not going to argue with you.
The problem becomes in writing grades because writing always has spiritual stakes as a matter of course, and instructors (the subjects of the subjectivity, as it were) are often oblivious to these stakes. The solution is to explain the stakes in terms that the subject can understand, which took me forever to learn how to do, because nobody explained it to me. That was annoying, but I'm not sure how that falls under subjectivity.
And yes, I find flippant behavior to be extremely irritating. It's disrespectful to the person being addressed and it's just cluttering the air with unnecessary words.