Misconstrue me a lunatic -- smear! (10)
I believe the answer is:
calumniate
'smear' is the definition.
('calumniate' can be a synonym of 'smear')
'misconstrue me a lunatic' is the wordplay.
'misconstrue' indicates an anagram (I've seen this in other clues).
'me'+'a'+'lunatic'='mealunatic'
'mealunatic' is an anagram of 'CALUMNIATE'.
(Other definitions for calumniate that I've seen before include "Insult" , "slander" , "Smear" .)