What does "that's my girl/boy" mean and when can I use it?
Native speaker’s answer
Rebecca
"That's my boy/girl" is an expression of encouragement or praise used with someone close, usually one's child. It's a bit uncommon to use it in situations not directed towards one's own child, unless you are very close friends. Ex: Wow, you got all As on your report card? That's my girl! Ex: A: Guys, I just graduated with Honors! B: That's my boy!