Teenager's party surrounded by beer smell (10)
I believe the answer is:
adolescent
'teenager's' is the definition.
('adolescent' can be a synonym of 'teenager')
'party surrounded by beer smell' is the wordplay.
'party' becomes 'do' (do is a kind of party).
'surrounded by' means one lot of letters goes inside another.
'beer' becomes 'ale' (I've seen this before).
'smell' becomes 'scent' (scent is a kind of smell**).
'do' placed within 'ale' is 'adole'.
'adole'+'scent'='ADOLESCENT'
(Other definitions for adolescent that I've seen before include "At the stage between childhood and maturity" , "juvenile" , "One growing" , "Immature" , "Developing" .)