Retsina being drunk is more unpleasant (7)
I believe the answer is:
nastier
'more unpleasant' is the definition.
('nasty' can be a synonym of 'unpleasant')
'retsina being drunk' is the wordplay.
'being drunk' is an anagram indicator.
'retsina' is an anagram of 'NASTIER'.
'is' acts as a link.
(Other definitions for nastier that I've seen before include "becomes more unpleasant" , "More unpleasant or distasteful" , "More horrid" , "more awkward" , "More damaging" .)