Feel remorse, being impolite with no defence (3)
I believe the answer is:
rue
'feel remorse' is the definition.
(I've seen this before)
'impolite with no defence' is the wordplay.
'impolite' becomes 'crude' (I've seen this in another clue).
'with no' suggests deleting specific letters.
'defence' becomes 'cd'.
'crude' with 'cd' taken out is 'RUE'.
'being' is the link.
(Other definitions for rue that I've seen before include "Cry" , "Repentant sort of shrub?" , "Regret or repent" , "show regret" , "Lament; a herb" .)