Problematic gift of cocaine polished off (8,7)
I believe the answer is:
poisoned chalice
'problematic gift' is the definition.
(supposed honour which actually poses problems)
'cocaine polished off' is the wordplay.
'off' indicates an anagram.
'cocaine'+'polished'='cocainepolished'
'cocainepolished' is an anagram of 'POISONED CHALICE'.
'of' is the link.
(Other definitions for poisoned chalice that I've seen before include "that was the death of Gertrude" , "may be a curse in disguise" , "This could have unfortunate consequences" , "evil in disguise" , "Source of trouble" .)