Other forms: bad eggs
Calling someone a bad egg is a mild, old-fashioned way to say he's a jerk. The school bully is a good example of a bad egg.
A bad egg is not a nice person — she's as unpleasant and disappointing as a literal bad, or spoiled, egg would be when you cracked it open. That's most likely where the figurative phrase came from, and it may have started as British public school slang. Other experts have found the earliest mentions of bad egg in American newspapers in the mid-1800's. There is also an English playground game called bad egg.