Taking off silver-plated brooch (5)
I believe the answer is:
aping
'taking off' is the definition.
(both can mean imitating or mocking)
'silver-plated brooch' is the wordplay.
'silver' becomes 'Ag' (Ag is the chemical symbol for silver).
'plated' indicates putting letters inside (plated can mean covered or coated).
'brooch' becomes 'pin' (decorative item pinned to clothing).
'ag' enclosing 'pin' is 'APING'.
(Other definitions for aping that I've seen before include "Acting like a parrot" , "Mimicking like monkey" , "Making copy of" , "Parroting" , "Sending up" .)