Down in the mouth
Definition 1 of 1
Pro Tip 1/3Colloquial Usage
It's casual language, more common in spoken English than in formal writing. 
After the game, Jake looked really down in the mouth.
Pro Tip 2/3Non-literal Meaning
'Down in the mouth' doesn't mean someone's mouth is physically pointing down, it's about their mood. 
Don't look so down in the mouth, the sun will come out tomorrow!
Pro Tip 3/3Facial Expression
The phrase often relates to someone's appearances suggesting sadness, not just their feelings. 
You've been down in the mouth all day, is there anything I can do to help?