Setter upset, beer upset! (8)
I believe the answer is:
embitter
'upset' is the definition.
(to embitter someone is to upset or anger them)
'setter upset beer' is the wordplay.
'setter' becomes 'me' (the setter of the clue).
'upset' says the letters should be written backwards.
'beer' becomes 'bitter' (bitter is a type of beer).
'me' reversed gives 'em'.
'em'+'bitter'='EMBITTER'
(Other definitions for embitter that I've seen before include "poison" , "Will exasperate" , "Make sour and resentful" , "Make resentful and hostile" , "Create resentment" .)