The speaker writes poetry for people she sill never see and for future generations. you can tell this is the answer by the phrase “unseen and unborn”.
Answer:
"Finally I kept silent, at first perhaps out of defiance, and then because I could neither think nor speak in your presence."
Explanation:
It seems it is somehow humorous because the man end up saying that if you can do it on your own, you can take the car to their place and they will do it for you.
It could not be angry or annoyed because he is willing to explain and he is even making a video about it.
As regards bitter, it does not fit as a possibility for the video or his explanation of the subject.