Asking her out is a withering experience! (9)
I believe the answer is:
shrinkage
'withering experience' is the definition.
'asking her out' is the wordplay.
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'asking'+'her'='askingher'
'askingher' is an anagram of 'SHRINKAGE'.
'is a' acts as a link.
(Other definitions for shrinkage that I've seen before include "theft from store?" , "Process of shrivelling or contracting" , "Process of becoming less" , "Reduction in volume" , "getting smaller" .)