It's fabulous smashing fascists, left and right (5,5)
I believe the answer is:
first class
'it's fabulous' is the definition.
'smashing fascists left and right' is the wordplay.
'smashing' indicates anagramming the letters.
'left' becomes 'l' (common abbreviation).
'and' is a charade indicator (letters next to each other) (I've seen this in other clues).
'right' becomes 'r' (common abbreviation).
'fascists'+'l'='fascistsl'
'fascistsl' after 'r' is 'rfascistsl'.
'rfascistsl' anagrammed gives 'FIRST-CLASS'.
(Other definitions for first class that I've seen before include "Top grade" , "A1" , "start to one's education" , "Of the highest grade" , "kindergarten?" .)