半瓶水響叮噹 [－－－响－当]

Jyutping bun3 ping4 seoi2 hoeng2 ding1 dong1
Pinyin bàn píng shuǐ xiǎng dīng dāng

Definitions (CC-CEDICT)
  1. lit. if you tap a half-empty bottle it makes a sound (idiom)
  2. fig. empty vessels make the most noise
  3. one who has a little knowledge likes to show off, but one who is truly knowledgeable is modest