Drunk head of organisation wears suit (3,2,2)
I believe the answer is:
out of it
'drunk' is the definition.
(I've seen this before)
'head of organisation wears suit' is the wordplay.
'head of' suggests taking the first letters.
'wears' indicates putting letters inside.
'suit' becomes 'outfit' (I've seen this before).
The initial letter of 'organisation' is 'o'.
'o' inserted inside 'outfit' is 'OUT OF IT'.
(Other definitions for out of it that I've seen before include "Excluded from participation" , "Eliminated" , "Without a chance" , "unaware of what's going on" , "Drunk < , unaware what is happening" .)