Expression used prior to mild rebuke is hardly a crime (2,7)
I believe the answer is:
no offence
'expression used prior to mild rebuke' is the definition.
I know nothing about this answer so I cannot judge whether this works.
'hardly a crime' is the wordplay.
'hardly' becomes 'no' (eg 'hardly a meal' means 'not a meal' or 'no meal').
'a crime' becomes 'offence' (offence is a kind of crime).
'no'+'offence'='NO OFFENCE'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for no offence that I've seen before include "legal" , "Don't be upset" .)