Dirty coat's first darned (6)
I believe the answer is:
cruddy
'dirty coat's first darned' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'dirty coat's first darned' is the wordplay.
'coat's' means to remove the middle letters (only the letters which coat the word are used).
'first' is a charade indicator (letters next to each other).
'darned' becomes 'crud' (I am not sure about this - if you are sure you should believe this answer much more).
'dirty' with its middle taken out is 'dy'.
'dy' put after 'crud' is 'CRUDDY'.
Can you help me to learn more?
(Other definitions for cruddy that I've seen before include "Filthy" , "Unpleasantly dirty" .)