一瓶子不响，半瓶子晃荡
yī​píng​zi​bù​xiǎng​bàn​píng​zi​huàng​dàng

empty vessels make the most noise

一瓶子不响，半瓶子晃荡 一瓶子不響，半瓶子晃蕩 yī​píng​zi​bù​xiǎng​bàn​píng​zi​huàng​dàng
empty vessels make the most noise
literally meaning a full bottle makes no sound while a half-filled bottle sloshes; used to describe people with little knowledge who like to show off