Only I am in bad mood, and I must make me look nice.
即使我心情不好，也必须让自己看起来很好。
Try to laugh out loud even though you are in bad mood.
即使你心情不好，也要尽情欢笑。
He was in bad mood, and showed no humor towards anyone.
他这几天心情不好，对人没好气儿。
Treat yourself better. Eating what you like when you are in bad mood.
对我自己好一点，心情不好的时候，什么都别考虑，赴吃我自己爱吃的吧。