bad apple
rotten apple

A rotten apple, the island will have no chance against us.

Five to six hundred is too many rotten apples, even among 38,000.

Well, he has experience with rotten apples, I'll say that for him.

I've known all along he's a rotten apple up to no good.

Just sort of a few rotten apples in the barrel.

Can we not understand that this is a rotten apple even before it joins?

"Maybe he was a rotten apple, and you never saw it."

"I've been in this business 20 years," he continued, "and you never know who the rotten apple is going to be."

More often than not, it seems, the rotten apples are the familiar names.

One rotten apple took some time to turn the rest bad.