"要想知道一个女孩的缺点，就去夸她的闺蜜们。"

Simplified Meaning:

When you compliment a girl in front of her friends, her friends may start talking about her flaws or mistakes. It's like when you tell someone that their coworker did a great job, and they respond by pointing out what the coworker did wrong. People often reveal what they really think or know about someone when they hear others getting praised because they might feel jealous, competitive, or resentful. So if you want to know someone's weaknesses, just say something nice about that person to their friends, and listen carefully to what they say. For example, in a school setting, if you tell a group of students that one of their classmates is very smart, some might start mentioning how that classmate always forgets their homework or struggles in another subject. This idea can teach us to be aware of how others might react to praise and to understand that people often share more about someone's true behavior or character in these moments.