A dead duck
Definition 1 of 2
Pro Tip 1/3Idiomatic Use
This phrase is a metaphor, not meant to describe an actual duck. 
After the scandal, the politician was a dead duck in his party.
Pro Tip 2/3Informal Context
Best used in casual conversations, not in formal writing or speeches. 
When the app crashed constantly, it became a dead duck.
Pro Tip 3/3Cultural Nuance
This phrase might be misunderstood in cultures where idiomatic expressions are uncommon. 
Make sure you explain what 'a dead duck' means to your foreign colleagues.