Most unexcited with ditty (4)
I believe the answer is:
tune
'ditty' is the definition.
(I've seen this in another clue)
'most unexcited with' is the wordplay.
'with' indicates a hidden word.
'TUNE' is hidden in the letters of 'most unexcited'.
(Other definitions for tune that I've seen before include "Melody; adjust (engine)" , "strain" , "Of engine, adjust to run smoothly" , "Adjust (car engine); air" , "'He who pays the piper calls the ...'" .)