Cute lad, a bore when naughty (8)
I believe the answer is:
adorable
'cute' is the definition.
(thesaurus)
'lad a bore when naughty' is the wordplay.
'when naughty' is an anagram indicator (I've seen this in other clues).
'lad'+'a'+'bore'='ladabore'
'ladabore' is an anagram of 'ADORABLE'.
(Other definitions for adorable that I've seen before include "Attractive - captivating" , "Broad lea (anag.)" , "Very pleasing" , "Very charming and attractive" , "worthy of love" .)