Cruel, miserable lives and habitual response (8)
I believe the answer is:
sadistic
'cruel' is the definition.
(thesaurus)
'miserable lives and habitual response' is the wordplay.
'miserable' becomes 'sad' ('sad' can be similar in meaning to 'miserable').
'lives' becomes 'is' ('be' can be a synonym of 'live').
'and' is a charade indicator (letters next to each other).
'habitual response' becomes 'tic' (I've seen this in other clues).
'sad'+'is'+'tic'='SADISTIC'
(Other definitions for sadistic that I've seen before include "Liking to inflict pain on others" , "Loving cruelty" , "Cruel and perverted" , "Deriving pleasure from inflicting pain" , "Gaining pleasure from inflicting pain" .)