Expression of disgust about leader of socialist party (4)
I believe the answer is:
bash
'party' is the definition.
(I've seen this before)
'expression of disgust about leader of socialist' is the wordplay.
'expression of disgust' becomes 'bah' (I've seen this before**).
'about' indicates putting letters inside.
'leader of' suggests taking the first letters.
The initial letter of 'socialist' is 's'.
'bah' going around 's' is 'BASH'.
(Other definitions for bash that I've seen before include "box" , "Party - clobber" , "knock" , "Criticise -- social gathering" , "Party (colloq.)" .)