Definition of a rotten or bad apple in English:

a rotten (or bad) apple

informal A bad or corrupt person in a group, typically one whose behavior is likely to have a detrimental influence on his or her associates.
[with reference to the effect that a rotten apple has on fruit with which it is in contact]
More example sentences
  • That's all I'm saying, is we have to start blaming the barrel and not simply saying there are a few bad apples who corrupted the barrel.
  • Still, aggressive masculine behaviour isn't the problem of a few bad apples.
  • Some reports list the officers and agencies responsible by name, but they are likely never to be considered bad apples, but only the custodians of a barrel that had some defects.
See parent entry: apple

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Word of the day apposite
Pronunciation: ˈapəzɪt
adjective
apt in the circumstances or relation to something