Being stuck up isn't exactly naughty (7)
I believe the answer is:
haughty
'being stuck up' is the definition.
(thesaurus)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for haughty that I've seen before include "Disdainful" , "Proud - self-satisfied" , "Imperious, arrogant" , "Showing arrogant superiority and disdain" , "Proud, arrogant" .)