Drunken Dirac unpleasantly sharp (5)
I believe the answer is:
acrid
'unpleasantly sharp' is the definition.
(I've seen this in another clue)
'drunken dirac' is the wordplay.
'drunken' is an anagram indicator.
'dirac' with letters rearranged gives 'ACRID'.
(Other definitions for acrid that I've seen before include "Bitter - caustic" , "Painfully pungent" , "Pungent or sharp, like smoke" , "Bitter - pungent" , "Pungent; caustic" .)