Repartee may be poor -- at home with a case of gangrene! (8)
I believe the answer is:
badinage
'repartee' is the definition.
(badinage is a kind of repartee)
'poor at home with a case of gangrene' is the wordplay.
'poor' becomes 'bad' ('bad' can be similar in meaning to 'poor'**).
'at home' becomes 'in' ('in' can be similar in meaning to 'at home').
'with' means one lot of letters go next to another.
'case of' says to hollow out the word (remove centre letters) (outsides of).
'gangrene' with its middle taken out is 'ge'.
'bad'+'in'+'a'+'ge'='BADINAGE'
'may be' acts as a link.
(Other definitions for badinage that I've seen before include "joking" , "Playful banter" , "Frivolous banter" , "Wordplay" , "Beg Diana with good-humoured teasing" .)