Chinese Proverbs -- 哪壶不开提哪壶

哪(nǎ)壶(hú)不(bù)开(kāi)提(tí)哪(nǎ)壶(hú) 

Touch the tender spot. It means to blurt out someone’s weakness or air somebody’s dirty laundry.

If a pot of water is not boiling, it does not make any (high-pitched) sound. This means figuratively that the pot of water is defective. If one deliberately picks up such a pot, then it figuratively means that one is deliberately publicizing somebody else's weaknesses or secrets. In English it is similar

壶(hú)=pot
提(tí)=pick up
不(bù)开(kāi)=not boiling

Example:
你真是哪壶不开提哪壶。 她就怕别人说她胖。
You are touching the tender spot. She is most sensitive to the topic of “being fat”.