Joke is quiet and offensive (5)
I believe the answer is:
prank
'joke' is the definition.
('prank' can be a synonym of 'joke')
'quiet and offensive' is the wordplay.
'quiet' becomes 'p' (music symbol for 'piano').
'and' is a charade indicator (letters next to each other).
'offensive' becomes 'rank' ('rank' can be similar in meaning to 'offensive'**).
'p'+'rank'='PRANK'
'is' acts as a link.
(Other definitions for prank that I've seen before include "High-spirited mischief" , "Jape" , "Mischievous trick" , "Mischievous act done for fun and amusement" , "Practical joke or trick" .)