Discourteous refusal inspired by poor rating (8)
I believe the answer is:
ignorant
'discourteous' is the definition.
(I've seen this before)
'refusal inspired by poor rating' is the wordplay.
'refusal' becomes 'no' (saying no to something).
'inspired by' means one lot of letters goes inside another (some letters breathed in or 'inspired' by others).
'poor' is an anagram indicator.
'rating' with letters rearranged gives 'igrant'.
'no' put within 'igrant' is 'IGNORANT'.
(Other definitions for ignorant that I've seen before include "Lacking in education" , "Ill-mannered" , "Unknowing" , "Devoid of knowledge" , "Poorly-educated" .)