Copy one friend drinking it (7)
I believe the answer is:
imitate
'copy' is the definition.
(I know that imitate is a more specific form of the action copy)
'one friend drinking it' is the wordplay.
'one' becomes 'i' (Roman numeral).
'friend' becomes 'mate' (mate is a kind of friend).
'drinking' indicates putting letters inside (inserted letters are consumed or drunk).
'mate' enclosing 'it' is 'mitate'.
'i'+'mitate'='IMITATE'
(Other definitions for imitate that I've seen before include "Copy or mimic" , "I tame it (anag)" , "Follow suit" , "Reproduce" , "I ate Tim! (anag.)" .)