Teacher interrupting robbery, a bon vivant (8)
I believe the answer is:
hedonist
'a bon vivant' is the definition.
(thesaurus)
'teacher interrupting robbery' is the wordplay.
'teacher' becomes 'don' (don is a kind of teacher).
'interrupting' is an insertion indicator.
'robbery' becomes 'heist' (heist is a kind of robbery).
'don' put into 'heist' is 'HEDONIST'.
(Other definitions for hedonist that I've seen before include "Thrill-seeker" , "seeker of fun" , "one enjoying himself" , "Self-indulgent type" , "He believes pleasure is the chief good in life" .)