Stunner squeezing fiance’s bottom is a poser (6)
I believe the answer is:
teaser
'poser' is the definition.
(thesaurus)
'stunner squeezing fiance's bottom' is the wordplay.
'stunner' becomes 'taser' (I've seen this before).
'squeezing' is an insertion indicator (squeeze can mean hug or embrace).
'fiance's bottom' becomes 'e' (I am not sure about this - if you are sure you should believe this answer much more).
'taser' placed around 'e' is 'TEASER'.
'is a' acts as a link.
Can you help me to learn more?
(Other definitions for teaser that I've seen before include "One who pulls someone's leg" , "inducement" , "One who annoys people or cards wool" , "Difficult question" , "Puzzling question or gentle goader" .)