Naughty date in French street (4)
I believe the answer is:
rude
'naughty' is the definition.
(thesaurus)
'date in french street' is the wordplay.
'date' becomes 'd' (common abbreviation eg in DOB, date of birth).
'in' means one lot of letters goes inside another.
'french street' becomes 'rue' (French for street or road**).
'd' inserted into 'rue' is 'RUDE'.
(Other definitions for rude that I've seen before include "Lacking civility" , "Impolite; unpolished" , "Impolite or vulgar" , "so curt here?" , "Impolite - simple" .)