Edible? It's gin, stupid -- it can't be eaten! (12)
I believe the answer is:
indigestible
'it can't be eaten' is the definition.
(something indigestible shouldn't be eaten)
'edible? it's gin stupid' is the wordplay.
'stupid' indicates an anagram (in a stupid order).
'edible'+'its'+'gin'='edibleitsgin'
'edibleitsgin' anagrammed gives 'INDIGESTIBLE'.
(Other definitions for indigestible that I've seen before include "can be hard to stomach" , "hard to take in" .)