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 am not sure about this - if you are sure you should give a lot more credence to this answer).
'wrapped in' indicates putting letters inside.
'offensive' becomes 'tet' (Tet Offensive, Vietnam War military campaign).
'ick' inserted within '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" .)