Foolish behaviour of idealists with no sort of memory (6)
I believe the answer is:
antics
'foolish behaviour' is the definition.
'idealists with no sort of memory' is the wordplay.
'idealists' becomes 'romantics' (romantic is a kind of idealist).
'with no' is a deletion indicator.
'sort of memory' becomes 'rom' (read-only memory).
'romantics' with 'rom' taken out is 'ANTICS'.
'of' acts as a link.
(Other definitions for antics that I've seen before include "Absurd behaviour intended to amuse" , "'Capers, pranks (6)'" , "Amusing behaviour" , "Absurd or foolish movements intended to amuse" , "comical capers" .)