In self-centred fashion, off I go, etc? I'll say! (12)

I believe the answer is:

egoistically

'in self-centred fashion' is the definition.

'off i go etc? i'll say' is the wordplay.
'off' indicates anagramming the letters.
'i'+'go'+'etc'+'ill'+'say'='igoetcillsay'
'igoetcillsay' anagrammed gives 'EGOISTICALLY'.

I've seen this clue in The Everyman puzzle in The Observer.

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