Sea change has popular couple displaying idiocy (7)
I believe the answer is:
asinine
'displaying idiocy' is the definition.
I can't tell whether this definition defines the answer.
'sea change has popular couple' is the wordplay.
'change' is an anagram indicator.
'has' is an insertion indicator.
'popular' becomes 'in' (something that's 'in' is fashionable).
'couple' shows that letters should be duplicated.
'sea' with letters rearranged gives 'ase'.
'in' duplicated is 'inin'.
'ase' enclosing 'inin' is 'ASININE'.
Can you help me to learn more?
(Other definitions for asinine that I've seen before include "simple" , "Extremely stupid or foolish" , "Really silly, ridiculous" , "'Mindless, vacuous (7)'" , "Donkey-like" .)