Idiot starts to Tweet "well, I regret purchase" (5)

I believe the answer is:

twirp

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'idiot' is the definition.
(I've seen this before)

'starts to tweet well i regret purchase' is the wordplay.
'starts to' says to take the initial letters.
'well i regret purchase' becomes 'wirp' (this might be a standard abbreviation of which I'm unaware).
The first letter of 'tweet' is 't'.
't'+'wirp'='TWIRP'

Can you help me to learn more?

(Another definition for twirp that I've seen is " Idiot".)

I've seen this clue in The Independent.

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