Playing duo that is in a way most unpleasant (7)
I believe the answer is:
snidest
'most unpleasant' is the definition.
Both the answer and definition are superlative adjectives. Perhaps you can see a link between them that I can't see?
'playing duo that is in a way' is the wordplay.
'playing duo' becomes 'nides' (I can't explain this - if you can you should believe this answer much more).
'that is in' is an insertion indicator.
'a way' becomes 'st' (abbreviation for street).
'nides' placed inside 'st' is 'SNIDEST'.
Can you help me to learn more?
(Other definitions for snidest that I've seen before include "most supercilious" , "most derogatory" .)