What's nasty in goody-goody, first to expect entitlement (9)
I believe the answer is:
privilege
'entitlement' is the definition.
(both can mean the right to do a particular thing)
'what's nasty in goody-goody first to expect' is the wordplay.
'what's nasty' becomes 'vile' (synonyms).
'in' indicates putting letters inside.
'goody-goody' becomes 'prig' (both can mean a sanctimonious person).
'first to' says to take the initial letters.
The initial letter of 'expect' is 'e'.
'vile' going within 'prig' is 'privileg'.
'privileg'+'e'='PRIVILEGE'
(Other definitions for privilege that I've seen before include "conditional benefit?" , "Special right" , "Class advantage" , "Prerogative" , "Advantage of one group denied to others" .)