: someone who creates problems or causes trouble for others
They'll look for telltale signs that your broker's a bad apple: too much trading … or investments that are clearly too risky for someone like you. Daniel McGinn
often, specifically: a member of a group whose behavior reflects poorly on or negatively affects or influences the remainder of the group
As in many industries, this could well be a case of a few bad apples tarnishing the reputation of the rest. Ian Giles
One bad apple in the bunch can destroy the cohesiveness of the team. Do-It-Yourself Retailing
… that individual brings down the rest of the team. This is the "one bad apple spoils the whole bunch" theory in action. Shep Hyken
Most people will be able to recall a situation where the bad mood or negative attitude of a colleague affected their workplace. As the saying goes, one bad apple spoils the whole damn bunch. Rebecca Jordan