Regretted, we hear, being discourteous (4)
I believe the answer is:
rude
'discourteous' is the definition.
(thesaurus)
'regretted we hear' is the wordplay.
'regretted' becomes 'rued' ('rue' can be a synonym of 'regret').
'we hear' indicates a 'sounds like' (homophone) clue.
'rued' is a homophone of 'RUDE'.
'being' is the link.
(Other definitions for rude that I've seen before include "dirty" , "Uncivil" , "Coarse or discourteous" , "Offensive; unpolished" , "Impolite or vulgar" .)