1.You can never teach an old dog new tricks. 老古董学不会新东西
You're never going to teach your father at the age of 79 to use a computer. You can't teach an old dog new tricks, you know.
不要指望教你79岁的老父亲学会电脑。年长的人学不会新事物。

2.meaner than a junkyard dog 冷漠，不友好
He is a man meaner than a junkyard dog.
他是一个残酷、冷漠的男人。

3.His bark is worse than his bite. 刀子嘴、豆腐心
I wouldn't be scared of her if I were you. Her bark's a lot worse than her bite.
如果我是你，我不会怕她。她是个刀子嘴，豆腐心的人。

4.let sleeping dogs lie 不要自找麻烦、自讨苦吃
Green is trying to let sleeping dogs lie.
格林在努力避免招惹是非。

5.the dog days of summer 一年中最热的三伏天
I can do nothing except for swimming in the dog days of summer.
在三伏天里，除了游泳，我什么事也做不成。

6.to rain cats and dogs 下倾盆大雨
In the middle of the picnic it started to rain cats and dogs, and everybody got soaked.
野餐进行到一半时，天开始下起大暴雨，每个人都湿透了。