Down in the mouth.? ? ? ? 垂頭喪氣，愁眉苦臉

Meaning - Sad or depressed. A person who is down in the mouth is probably showing visible signs of unhappiness.

Why is he so down in the mouth?

His ex-girlfriend is dating his brother!

他為什么垂頭喪氣的？

（因為）他前女友和他兄弟在一起了。