I'm terrible at these.
Someone just told me, the cow ate the cabbage, which means telling somebody off I think and draining the ocean with an eyedropper, which means doing the imposter .
As I am often up very late, somebody once said to me that I burn the midnight oil. I said, no I don't drink! I thought burning the midnight oil meant staying up and getting drunk. 
As I speak other languages, I have learned plenty in those as well. One of my favorites can be translated as if I know, I guy. Basically it means I have no idea.
I know there is a Chinese expression that translates as eat bitterness, but I forgot the actual expression, it means you have to sacrifice things.