bàn​píng​shuǐ​xiǎng​dīng​dāng

empty vessels make the most noise

半瓶水响叮当 半瓶水響叮噹 bàn​píng​shuǐ​xiǎng​dīng​dāng
empty vessels make the most noise
Literally means a half-empty bottle makes a loud sound; used as an idiom to describe a person who has only a little knowledge but likes to show it off, while those who are truly knowledgeable remain modest