General manager must be in -- it's a terrible shame (6)
I believe the answer is:
stigma
'shame' is the definition.
(stigma can mean shame or disgrace)
'general manager must be in it's a terrible' is the wordplay.
'general manager' becomes 'GM' (abbreviation).
'must be in' indicates putting letters inside.
'terrible' indicates anagramming the letters.
'its'+'a'='itsa'
'itsa' anagrammed gives 'stia'.
'gm' put inside 'stia' is 'STIGMA'.
(Other definitions for stigma that I've seen before include "Mark of infamy or disgrace" , "Symbol of disgrace or infamy" , "Mark of shame, stain on reputation" , "Mark of shame or social disgrace" , "part of plant" .)