Miscreant left after vandalising car I'm in (8)
I believe the answer is:
criminal
'miscreant' is the definition.
(thesaurus)
'left after vandalising car i'm in' is the wordplay.
'left' becomes 'l' (common abbreviation).
'after' means one lot of letters go next to another.
'vandalising' indicates an anagram (I've seen 'vandalised' mean this).
'car'+'im'+'in'='carimin'
'carimin' is an anagram of 'crimina'.
'l' after 'crimina' is 'CRIMINAL'.
(Other definitions for criminal that I've seen before include "Offender" , "Felon, malefactor" , "Punishable by law" , "An habitual breaker of the law" , "Felon, lawbreaker" .)