Complacent son getting cup (4)
I believe the answer is:
smug
'complacent' is the definition.
(smug can mean complacent or self-satisfied)
'son getting cup' is the wordplay.
'son' becomes 's' (genealogical abbreviation for son).
'getting' says to put letters next to each other.
'cup' becomes 'mug' (I've seen this before).
's'+'mug'='SMUG'
(Other definitions for smug that I've seen before include "Self-righteous" , "irritating expression" , "Conceited and self-satisfied" , "Irritatingly self-satisfied" , "Prim" .)