We hear they regretted being impolite (4)
I believe the answer is:
rude
'impolite' is the definition.
(similar in meaning)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for rude that I've seen before include "Insolent" , "Impolite or coarse" , "Ill-mannered; hearty" , "Impertinent" , "Ill-mannered and coarse" .)