Lacking drink before party? Impossible! (2,3,2)
I believe the answer is:
no can do
'impossible' is the definition.
('no can do' can mean something is impossible)
'lacking drink before party?' is the wordplay.
'lacking' becomes 'no' (eg lacking money means with no money).
'drink' becomes 'can' (eg a can of beer).
'before' means one lot of letters go next to another.
'party?' becomes 'do' (do is a kind of party).
'no'+'can'+'do'='NO CAN DO'
(Other definitions for no can do that I've seen before include "Informal expression of refusal" , "That's not possible" , "Absolutely not!" , "Unable to help" , "That's out of the question!" .)