Rude expression mugs rival off (9)

I believe the answer is:

vulgarism

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'rude expression' is the definition.
The answer and definition can be both human attributes as well as being singular nouns.
Maybe they are linked in a way I don't understand?

'mugs rival off' is the wordplay.
'off' indicates anagramming the letters.
'mugs'+'rival'='mugsrival'
'mugsrival' is an anagram of 'VULGARISM'.

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I've seen this clue in The Independent.

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