Midwestern/northern American English: 

"It's raining cats and dogs" refers to a heavy downpour that startles cats and dogs from their ledges they were resting on. I've never seen a dog fall or jump down but I have seen cats fall or jump from gutters or trees whose branches are giving way to the storm. It's quite funny!

"They made it by the skin of their teeth.."

This means they barely finished something with no time or space to spare. 

"Gag me with a spoon."

This is a response to something so gross that being forced to vomit with a spoon in the back of your throat, would be relief to the disgust. 

If you'd like to read some hilarious ones then look up some by "The Cable guy." One by him is, "madder than an albino hitch-hiking in a snow storm." 

"I'm stuffed like a turkey" traditionally, a holiday turkey is stuffed until it's overflowing, with other foods before roasting.

"Hit the hay" = go to bed/sleep for the night. 

"He's got one foot nailed to the floor" = they are not accomplishing anything and repeating what they've already done. 

"Two left feet"= clumsy, especially in dancing. 

"You're crazier than a Junebug!" This is not an insult but a laughing response to someone who does something daring, due to their own mischevious lack of caution. Beetles that come out in June, fly about, seeming happy, and run right into things and then continue to fly around into something else, as if they're drunk. Playing a light hearted prank with the threat of mild retaliation, is a good example. This expression came from a rural scenario. So an example would be cow tipping! 

People who living in glass rooms never throw stones. I learned it on BBC.

In Chinese, 己所不欲，勿施于人。

 In my words, don't enforce others do things you don't like.