When proudly displayed, revealed to be bad (5,3)

I believe the answer is:

shown off

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'when proudly displayed' is the definition.
The answer and definition can be both to do with perception as well as being past participle verbs.
Perhaps they are linked in a way I don't understand?

'revealed to be bad' is the wordplay.
'revealed' becomes 'shown' (I've seen this in another clue).
'to be bad' becomes 'off' (eg meat that's gone off is bad).
'shown'+'off'='SHOWN OFF'

Can you help me to learn more?

I've seen this clue in the Evening Standard.

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