Source of irritation for man from Dacha showing off energy
I believe the answer is:
headache
'off energy' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'source of irritation for man from dacha' is the wordplay.
'source of irritation' becomes 'e' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'for' is a charade indicator (letters next to each other) (I've seen this in other clues).
'man' becomes 'he'.
'from' indicates anagramming the letters (from the letters).
'dacha' with letters rearranged gives 'adach'.
'he'+'adach'='headach'
'e' after 'headach' is 'HEADACHE'.
'showing' is the link.
Can you help me to learn more?
(Other definitions for headache that I've seen before include "Source of worry (and pain!)" , "big problem" , "Cause of worry/trouble" , "Informally a worrying problem - take an asprin" , "Pain in the cranium" .)