Self-satisfied, having rejected sweets (4)
I believe the answer is:
smug
'self-satisfied' is the definition.
('smug' can be a synonym of 'self-satisfied')
'rejected sweets' is the wordplay.
'rejected' is a reversal indicator.
'sweets' becomes 'gums' (gum is a kind of sweet).
'gums' in reverse letter order is 'SMUG'.
'having' acts as a link.
(Other definitions for smug that I've seen before include "Like a stuffed shirt" , "Smirking" , "Overly complacent" , "Be envious of" , "Self-righteous" .)