In AA to meet drunk individually (3,2,1,4)
I believe the answer is:
one at a time
'individually' is the definition.
(I've seen this before)
'in aa to meet drunk' is the wordplay.
'drunk' is an anagram indicator.
'in'+'aa'+'to'+'meet'='inaatomeet'
'inaatomeet' with letters rearranged gives 'ONE AT A TIME'.
(Other definitions for one at a time that I've seen before include "Individually" , "A-team, I note, travelling separately" , "Singly" .)