The teach it back methodology is a good way to learn.
Demonstrate to the students. Then have them practice it.
Then work with them each and ask them to show you and ask them to talk it through.
This will actually help the student learn to be a teacher before the get their black belt.
The issue with this is that lower belts can do something OK for lower ranks and then be frustrated when more or slightly different is expected at a higher rank.
You will make mistakes.
There will always be at least one student you will show them. And then when the senior Black belt asks they will not be able to do it or answer even though they just did it. Their failure is not yours. How you handle their failure is yours.
Do not let it eat at you.
Do not get mad and punish the class for that one.
It is ok to say I don't know. let me get back to you.
It could be later in class or the next class or after you discuss with another instructor.
I have found those that yell louder and go faster when frustrated that the students are not getting it are not teaching.
As to telling an instructor to pound sand, I would approach it differently.
I would try it his way at first. He may have a method. e.g. checking for raw talent and or how much you absorbed during your training.
He may have some other senior color belts he will ask how you did.
Do not think this is bad.
He is looking to find what he needs to work with you.
Look at it as a position of trust. They are trusting you with their students.
They would not have asked if they thought you could not do it at all.
Now if they get mad, or have unreal expectations of perfection then you can have a serious discussion with yourself on what to do next.
Best of Luck