A bit crotchety? Nonsense! (3)
I believe the answer is:
rot
'nonsense' is the definition.
(rot can mean nonsense or rubbish)
'a bit crotchety?' is the wordplay.
'a bit' indicates the answer is hidden within the clue (I've seen 'bit of' mean this).
'ROT' is hidden in the letters of 'crotchety'.
(Other definitions for rot that I've seen before include "Decay in grotesque way" , "Corruption" , "Decay - rubbish" , "Decomposition" , "Gradual decline" .)