Make unattractive date seem otherwise with gin! (11)
I believe the answer is:
demagnetise
'make unattractive' is the definition.
(I've seen this before)
'date seem otherwise with gin' is the wordplay.
'otherwise with' indicates anagramming the letters.
'date'+'seem'='dateseem'
'dateseem' anagrammed with 'gin' gives 'DEMAGNETISE'.
(Other definitions for demagnetise that I've seen before include "Make unattractive" , "Remove Poles" , "Degauss" .)