bad friend; undesirable companion; bad influence
Refers to a friend who is a bad influence or leads one astray. Often used in contrast with 良友 (good friend).
See also: 良友
He often goes out at night, led astray by his bad friends.
They say that if you keep company with bad friends, you'll become bad yourself.
partner in crime; close friend; buddy
Jocular or affectionate term for a close friend with whom one shares mischief or secrets. Not truly negative; implies a bond through shared (often minor) misbehavior.
He's been my partner in crime since our school days, and we still hang out a lot.
I stayed up late playing games with my buddies.