Coffee face refers to the ugly face people have in the morning before they drink their coffee. They will be much better once they have a cup of coffee.

“咖啡脸”指的是人早晨还没喝咖啡前摆出的一张臭脸。只需喝一杯咖啡他们就会好得多。

Some people need a cup of strong coffee or tea in the morning to wake them up, without the caffeine in the drinks they will feel listless and irritable. 

有些人早上起来需要喝一杯浓咖啡或浓茶才能清醒，没有这些饮料中的咖啡因他们就会感觉无精打采，而且烦躁易怒。

Example: 

Husband: Honey you look awful. Are you coming down with something?

丈夫：亲爱的你的脸色看起来很糟。发生什么事了吗？

Wife: No, it's just my coffee face. Brew some coffee for me.

妻子：没什么，这不过是我的“咖啡脸”而已。给我煮点咖啡吧。