Doing one's nut up? (3,4)
I believe the answer is:
air rage
'nut up?' is the definition.
The definition suggests a singular noun which matches the answer.
'doing one's' is the wordplay.
I cannot really understand how this works, but
'doing' could be 'rag' (rag is a kind of doing) and 'rag' is found in the answer.
'one' could be 'i' (Roman numeral) and 'i' is found within the answer.
The remaining letters 'are' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for air rage that I've seen before include "high aggression" , "heightened anger?" .)