Crossword Genius

Fruitcake can't use bananas (7)

Ross

I believe the answer is:

nutcase

'fruitcake' is the definition.
(I've seen this before)

'can't use bananas' is the wordplay.
'bananas' indicates an anagram (informal term for mad).
'cant'+'use'='cantuse'
'cantuse' with letters rearranged gives 'NUTCASE'.

(Other definitions for nutcase that I've seen before include "fool" , "Crank" , "Loony" , "Psycho" , "Eccentric" .)

I've seen this clue in The Independent.
Want a hint initially instead of a full solution? Install my app