Fatheads' afterthought for a friend (6)

I believe the answer is:

chumps

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'fatheads' afterthought for a friend' is the definition.
I can't judge whether this defines the answer.

'afterthought for a friend' is the wordplay.
'afterthought' becomes 'ps' (as in a PS in a letter).
'for' means one lot of letters go next to another (I've seen this in other clues).
'a friend' becomes 'chum' (chum is a kind of friend).
'ps' after 'chum' is 'CHUMPS'.

Can you help me to learn more?

(Another definition for chumps that I've seen is " Fools".)

I've seen this clue in the Evening Standard.

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