Nits are possibly more unpleasant (7)
I believe the answer is:
nastier
'more unpleasant' is the definition.
('nasty' can be similar in meaning to 'unpleasant')
'nits are possibly' is the wordplay.
'possibly' indicates anagramming the letters.
'nits'+'are'='nitsare'
'nitsare' is an anagram of 'NASTIER'.
(Other definitions for nastier that I've seen before include "More damaging" , "more awkward" , "Less pleasant" , "Getting even worse" , "Less nice" .)