Snooty is up, or clue is misleading (12)
I believe the answer is:
supercilious
'snooty' is the definition.
(thesaurus)
'is up or clue is misleading' is the wordplay.
'misleading' indicates an anagram (I've seen this in other clues).
'is'+'up'+'or'+'clue'+'is'='isuporclueis'
'isuporclueis' is an anagram of 'SUPERCILIOUS'.
(Other definitions for supercilious that I've seen before include "Arrogant and disdainful" , "Condescending" , "Disdainful, haughty" , "Contemptuously superior" .)