Conceited cities gloat appallingly (11)
I believe the answer is:
egotistical
'conceited' is the definition.
(I know that conceited can be written as egotistical)
'cities gloat appallingly' is the wordplay.
'appallingly' is an anagram indicator (I've seen this in other clues).
'cities'+'gloat'='citiesgloat'
'citiesgloat' with letters rearranged gives 'EGOTISTICAL'.
(Other definitions for egotistical that I've seen before include "Selfish" , "Conceited and boastful" , "Excessively conceited" , "Self-important" , "Highly self-absorbed" .)