good egg

Probably a humorous antonym of bad egg (“someone whose behaviour is reprehensible or irresponsible; a rogue”).

• "The chemist and the bacteriologist gave him the third degree and, like most criminals, it was found difficult to tell just when a good egg began to be bad, and it appeared that it depended largely on how he was handled, especially in his youth, […]"
• "Tom speaks: "I have a girl friend I want you to meet. She's a good egg.""
• "Johnny Parker is in town. I like Johnny. He's a big shot in pictures and he's a good egg."
• "In contrast, Saito […] was one of the good eggs … He would let us rest whenever the coast was clear and even shared the odd cigarette."
• ""And the fifth immortal we know tried to kill you." "He is a bad egg. We stick to good''' eggs.""
• "Drogon sniffs Jon [Snow]—and Dany [Daenerys Targaryen] apparently doesn't care enough about Jon's life to get off Drogon so she can witness their interaction on the other side of his fat neck and make sure her son isn't eating his cousin—and seems to sense he's a good egg at the least and quite possibly that he's a Targaryen."

• bad egg