No performance? Hell be disappointed! (7)
I believe the answer is:
showoff
'no' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'performance? hell be disappointed' is the wordplay.
I cannot quite understand how this works, but
'performance?' could be 'show' (performance is a kind of show) and 'show' is present in the answer.
The remaining letters 'off' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Another definition for showoff that I've seen is " Exhibitionist".)