Rarefied courtesies renounced by you and me, rebelliously (8)
I believe the answer is:
esoteric
'rarefied' is the definition.
(I've seen this in another clue)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for esoteric that I've seen before include "I set core up to be mysterious" , "not generally understood" , "Hard to understand" , "Intelligible only with special knowledge" , "Secret, mysterious" .)