Mostly offensive, wrapped in offensive label (6)
I believe the answer is:
ticket
'label' is the definition.
(thesaurus)
'mostly offensive wrapped in offensive' is the wordplay.
'mostly offensive' becomes 'ick' (I can't explain this - if you can you should give a lot more credence to this answer).
'wrapped in' means one lot of letters goes inside another.
'offensive' becomes 'tet' (Tet Offensive, Vietnam War military campaign).
'ick' going into 'tet' is 'TICKET'.
Can you help me to learn more?
(Other definitions for ticket that I've seen before include "It entitles the bearer, to enter perhaps" , "Buy one for admittance" , "Authority for entry, etc" , "lottery entry" , "Authorisation for travel, theatre etc" .)