Rebuke what people eschewing formal attire do (5,4)
I believe the answer is:
dress down
'rebuke' is the definition.
(I know that rebuke can be written as dress down)
'people eschewing formal attire do' is the wordplay.
I cannot really understand how this works, but
'formal' could be 'dress' (similar in meaning) and 'dress' is found in the answer.
'do' is found in the answer.
This explanation may well be incorrect...
'what' acts as a link.
Can you help me to learn more?
(Other definitions for dress down that I've seen before include "inappropriate state of attire" , "Wear informal attire" , "Be unsuited" , "Put on casual clothes" , "Rebuke" .)