Couplet oaf composed is inappropriate (3,2,5)
I believe the answer is:
out of place
Here is my best explanation:
'inappropriate' is the definition.
'couplet oaf composed' is the subsidiary indication.
'composed' is an anagram indicator.
'coupletoaf' anagrammed gives 'outofplace'.
'is' is the link.
(Another definition for out of place that I've seen is "Not suited to the occasion".)