Surprised when kissed on the lips? (10)
I believe the answer is:
gobsmacked
'surprised' is the definition.
'kissed on the lips?' is the wordplay.
'kissed' becomes 'smacked' (a smacker is a loud kiss).
'on' is a charade indicator (letters next to each other).
'the lips?' becomes 'gob' (both can mean the mouth).
'smacked' after 'gob' is 'GOBSMACKED'.
'when' acts as a link.
(Other definitions for gobsmacked that I've seen before include "bowled over" , "Astounded" , "utterly astonished" , "Stunned" , "Flabbergasted" .)