It's not nice for half of us to be in the red, badly (4)
I believe the answer is:
rude
'it's not nice' is the definition.
I can't judge whether this definition defines the answer.
'half of us to be in the red badly' is the wordplay.
'half of' suggests halving the letters.
'to be in the' means one lot of letters goes inside another.
'badly' indicates an anagram (letters in the wrong order).
'us' with half the letters taken is 'u'.
'red' anagrammed gives 'rde'.
'u' inserted into 'rde' is 'RUDE'.
'for' is the link.
Can you help me to learn more?
(Other definitions for rude that I've seen before include "Impolite - simple" , "Uncivilised" , "Impudent" , "Blue" , "Impertinent" .)