Blair's dodgy dossier initially offensive (6)
I believe the answer is:
ribald
'offensive' is the definition.
(thesaurus)
'blair's dodgy dossier initially' is the wordplay.
'dodgy' indicates an anagram.
'initially' indicates taking the first letters.
The first letter of 'dossier' is 'd'.
'blair' is an anagram of 'ribal'.
'ribal'+'d'='RIBALD'
(Other definitions for ribald that I've seen before include "near the knuckle" , "Coarsely mocking" , "Indecent" , "Humorous in vulgar or disrespectful way" , "Mean" .)