Stunning wine put into wrong glass at first (8)
I believe the answer is:
shocking
'stunning' is the definition.
('shock' can be a synonym of 'stun')
'wine put into wrong glass at first' is the wordplay.
'wine' becomes 'hock' (hock is a kind of wine).
'put into' means one lot of letters goes inside another.
'wrong' becomes 'sin' (I've seen this before**).
'at first' says to take the initial letters.
The initial letter of 'glass' is 'g'.
'hock' put into 'sin' is 'shockin'.
'shockin'+'g'='SHOCKING'
(Other definitions for shocking that I've seen before include "Appalling, causing disgust" , "Awful - ghastly" , "Causing disgust; very bad" , "Traumatic" , "Dreadful (shade of pink?)" .)