A threesome firmly quashed — loser, big time! (7,2,3,4)
I think it could be either:
slimmer of the year
If this is the answer, I'm afraid I cannot explain it.
(Other definitions for slimmer that I've seen before include "thinner" , "with less fat" , "More slenderly built" , "One attempting to lose weight" , "in better shape?" .)
'loser big time' is the definition.
'a threesome firmly quashed' is the wordplay.
'quashed' indicates anagramming the letters (quash can mean to smash up).
'a'+'threesome'+'firmly'='athreesomefirmly'
'athreesomefirmly' anagrammed gives 'SLIMMER OF THE YEAR'.