Happy expression with a drink, about right! (4)
I believe the answer is:
grin
'happy expression' is the definition.
(I've seen this before)
'a drink about right' is the wordplay.
'a drink' becomes 'gin' (gin is a kind of drink).
'about' means one lot of letters goes inside another.
'right' becomes 'r' (common abbreviation).
'gin' placed around 'r' is 'GRIN'.
'with' acts as a link.
(Other definitions for grin that I've seen before include "Happy expression" , "Accept with good grace - . . . . and bear it" , "Ring (anag.)" , "Smile broadly showing teeth" , "A broad smile showing the teeth" .)