Spurn buns being returned (4)
I believe the answer is:
snub
'spurn' is the definition.
(snubbing is a kind of spurning)
'buns being returned' is the wordplay.
'being returned' is a reversal indicator.
'buns' back-to-front is 'SNUB'.
(Other definitions for snub that I've seen before include "Rebuff insultingly" , "Give (someone) the cold shoulder" , "Rude put-down; blunt (nose)" , "Deliberate insult" , "16" .)