Fatheads' afterthought for a friend (6)
I believe the answer is:
chumps
'fatheads' afterthought for a friend' is the definition.
I can't tell whether this defines the answer.
'afterthought for a friend' is the wordplay.
'afterthought' becomes 'ps' (ps stands for postscript).
'for' is a charade indicator (letters next to each other) (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".)