Anger reflected by very wearing bad mood (7)
I believe the answer is:
vinegar
'bad mood' is the definition.
(vinegar can mean sourness or grumpiness)
'anger reflected by very wearing' is the wordplay.
'anger' becomes 'rage' (rage is a kind of anger).
'reflected' says the letters should be written in reverse.
'by' is a charade indicator (letters next to each other).
'very wearing' becomes 'vin' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'rage' written backwards gives 'egar'.
'egar' put after 'vin' is 'VINEGAR'.
(Other definitions for vinegar that I've seen before include "Acetic acid" , "Condiment - bad temper" , "Sour stuff" , "Sour liquid used as condiment" , "Liquid used as condiment or food preservative" .)