Stop consuming German sausage loudly -- it's what losers do (4,3,5)
I believe the answer is:
come off worst
'what losers do' is the definition.
(to come off worst is to lose)
'stop consuming german sausage loudly' is the wordplay.
'stop consuming' becomes 'come off' (to come off a particular food is to give it up).
'german sausage' becomes 'wurst' (I've seen this in another clue).
'loudly' indicates a 'sounds like' (homophone) clue (when spoken - not silently).
'wurst' is a homophone of 'worst'.
'comeoff'+'worst'='COME OFF WORST'
'it's' acts as a link.
(Another definition for come off worst that I've seen is " Do least well".)