be walking on eggshells

To be acting with great care and consideration so as not to upset someone. The littlest thing tends to anger my mother, so I feel like I'm always walking on eggshells whenever I'm at her house. I've been walking on eggshells while giving my employees their performance reviews because I know how devastating a bad one can be. A: "I hope you were careful in there—those lobbyists have the power and influence to do some serious damage to your career." B: "Don't worry, I was walking on eggshells the whole time."