gang of hoodlums; bad company; delinquent friend
Refers to a group of juvenile delinquents or a friend who is a bad influence. Often used in contexts of youth crime or peer pressure.
He hangs out with a gang of hoodlums and stays out late at night.
I was led astray by bad company and ended up shoplifting.
不良 alone means 'delinquent' or 'bad behavior'; 不良仲間 specifically refers to the group or companion aspect.
仲間 is a neutral term for 'companion' or 'group'; 不良仲間 adds the negative 'delinquent' nuance.
Compound of 不良 (delinquent, bad) and 仲間 (companion, group). The exact historical derivation is uncertain, but the combination straightforwardly means 'delinquent companion/group'.