On one occasion having interrupted, referred to as egocentric (9)
I believe the answer is:
conceited
'egocentric' is the definition.
(thesaurus)
'on one occasion having interrupted referred to' is the wordplay.
'on one occasion' becomes 'once' (synonyms).
'having interrupted' means one lot of letters goes inside another.
'referred to' becomes 'cited' ('cite' can be a synonym of 'refer to').
'once' put into 'cited' is 'CONCEITED'.
'as' acts as a link.
(Other definitions for conceited that I've seen before include "Arrogant" , "Vain, having swelled head" , "Very proud of oneself" , "full of himself" , "Stuck-up" .)