Definition
This idiom is used to retort when someone criticizes you for a fault or behavior that they themselves exhibit.
你也不一样！
"You're always late!" "Oh, look who's talking!"
“你总是迟到！”“哦，看看是谁在说话！”
He called me a big spender? Look who's talking!
他叫我大花钱？看看是谁在说话！
"You should exercise more," she said, look who's talking, she never goes to the gym.
“你应该多运动，”她说，看看是谁在说话，她从不去健身房。