Reacting badly to display of ill grace (8)
I believe the answer is:
allergic
'reacting badly' is the definition.
(I've seen this before)
'of ill grace' is the wordplay.
'of' indicates anagramming the letters (the answer comes from or 'of' the letters).
'ill'+'grace'='illgrace'
'illgrace' anagrammed gives 'ALLERGIC'.
'to display' is the link.
(Other definitions for allergic that I've seen before include "Vulnerable or sensitive to, perhaps pollen" , "Hypersensitive (to certain substances)" , "Having an adverse reaction (to something)" , "Reacting badly (to something)" , "Reacting badly to certain things" .)