His gown is ruffled -- rotten exhibitionism! (7-3)

I believe the answer is:

showing off

'exhibitionism' is the definition.
(thesaurus)

'his gown is ruffled rotten' is the wordplay.
'is ruffled' indicates anagramming the letters.
'rotten' becomes 'off' (rotten food is 'off').
'his'+'gown'='hisgown'
'hisgown' with letters rearranged gives 'showing'.
'showing'+'off'='SHOWING OFF'

(Another definition for showing off that I've seen is " Behaving ostentatiously".)

I've seen this clue in The Telegraph.

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