合不攏嘴 [－－拢－]

Jyutping hap6 bat1 lung5 zeoi2
Pinyin hé bù lǒng zuǐ

Definitions (CC-CEDICT)
  1. unable to conceal one's happiness, amazement, shock etc
  2. grinning from ear to ear
  3. mouth agape
  4. gobsmacked