Endures horrible son showing incivility (8)
I believe the answer is:
rudeness
'incivility' is the definition.
(I've seen this before)
'endures horrible son' is the wordplay.
'horrible' indicates an anagram.
'son' becomes 's' (genealogical abbreviation for son).
'endures' anagrammed gives 'rudenes'.
'rudenes'+'s'='RUDENESS'
'showing' is the link.
(Other definitions for rudeness that I've seen before include "Discourtesy" , "Impolite behaviour" , "Bad manners, lack of politeness" , "Lip" , "loutish behaviour" .)