Fond of an upset occasionally (2,3,3)
I believe the answer is:
on and off
'occasionally' is the definition.
(I've seen this before)
'fond of an upset' is the wordplay.
'upset' indicates an anagram.
'fond'+'of'+'an'='fondofan'
'fondofan' with letters rearranged gives 'ON AND OFF'.
(Other definitions for on and off that I've seen before include "Occasionally" , "From time to time, not continually" , "spasmodic" , "Switch choices" , "Now and then, starting and stopping" .)