黑狗源自于丘吉尔的一句话：“心中的抑郁就像只黑狗，一有机会就咬住我不放。”
从此，“black dog”便成了抑郁症的代名词!所以，在英语中black dog有“沮丧”“情绪低落” “意志消沉”之意。
black dog
沮丧，意气消沉，抑郁
I feel a black dog coming on whenever I get school.
一想到要上学我就心情低落。
☆I've got a black dog in me.
我心情不太好。
关于“dog”的相关英语表达
yellow dog
卑鄙的人
You are a yellow dog!
你是一个忘恩负义的人!
In spite of the fact that you treat him very well, he is a yellow dog.
尽管事实上你对他非常好，但是他仍然是个卑鄙的人。
【注意】：是否是俚语的意思，要根据语境来，比如下面这两句都是指字面意思的“黄狗”：
She has a yellow dog.
她有一只黄色的狗。
It's a yellow dog.
它是一只黄色的狗。
dog eat dog
残酷无情的竞争，自相残杀
It's like a dog eat dog world.
这是个残酷的世界。
With shrinking markets, it's dog eat dog for every company in this field.
由于市场的萎缩，这些公司展开了你死我活的竞争。
hot dog
太棒了
【我们都知道“hot dog”是“热狗”，但它除了“热狗”，还可以表示惊讶或兴奋的语气，译为“太棒了”，是美国人长用的一句习语。】
- I won the competition.
- Hot dog!
我赢得了这次比赛!太棒了!
Hot dog! I can't wait to try out my new motorbike!
太棒了!我迫不及待想去试试我的新摩托车!
a dog's life
潦倒的生活，非常悲惨的生活
His father's bankruptcy led him a dog's life.
他父亲的破产使他过上了困苦的日子。
Poor Mike, his wife leads him a dog's life with her incessant nagging.
可怜的迈克，他妻子唠叨不休，使他过着不安宁的日子。
in the dog house
大事不妙
He is in the dog house with his boss.
他被老板冷落了。
The police caught her driving without a license. I guess she's in the dog house now.
警察逮到她无照驾驶。我想她现在麻烦大了。
