Definition of a rotten (or bad) apple in English:

a rotten (or bad) apple

phrase

informal
  • A bad or corrupt person in a group, especially one whose behaviour is likely to have a detrimental influence on the others.

    ‘chartered accountants have no time for rotten apples in their professional barrel’
    ‘looks like we hired ourselves a bad apple’
    • ‘A few more bad apples will be identified, they'll be suspended with pay and the allegations against them will be disposed of in some way or another.’
    • ‘In reply he got the by now standard answer that there are crooks in all professions and the few bad apples must not be allowed to contaminate the image of the entire barrel.’
    • ‘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.’
    • ‘We're human and out of any group of people there are bad apples.’
    • ‘Still, aggressive masculine behaviour isn't the problem of a few bad apples.’
    • ‘What he did in his speech last week was take the bad apple approach and say OK, what we're going to do is we're going to stiffen the penalties on the bad apples.’
    • ‘If one restaurant is doing badly it doesn't have access to the bank accounts of the other restaurants and thus there is no way for the bad apples to drag down the barrel.’
    • ‘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.’
    • ‘But you can't weed out the bad apples by merely having a national I.D. card.’
    • ‘It is far more realistic to turn your complaining inward, and pressure the bad apples in your group to stop pulling down the average.’