Blatant just to drink beforehand (9)
I believe the answer is:
downright
'blatant' is the definition.
(I've seen this before)
'just to drink beforehand' is the wordplay.
'just' becomes 'right' (similar in meaning).
'to drink' becomes 'down' (to down something can mean to drink it quickly).
'beforehand' says to put letters next to each other.
'right' put after 'down' is 'DOWNRIGHT'.
(Other definitions for downright that I've seen before include "rank" , "Plain-spoken" , "blunt" , "Utter, complete" , "Utter, arrant" .)