Regretted, say, being coarse (4)
I believe the answer is:
rude
'coarse' is the definition.
(I've seen this in another clue)
'regretted say' is the wordplay.
'regretted' becomes 'rued' ('rue' can be a synonym of 'regret').
'say' shows a homophone (sound like).
'rued' sounds like 'RUDE'.
'being' is the link.
(Other definitions for rude that I've seen before include "Discourteous or unrefined" , "Robust - roughly made" , "Impolite - obscene" , "so curt here?" , "'Bad-mannered, discourteous (4)'" .)