Selling it as soon as you've bought it — Chinese expression

Question

In college, I had just started a physics class in relativity and I was so excited that I began explaining everything I had learned to my Taiwanese roommate. Perhaps my tone was a bit too arrogant or lecturing, because he became irritated and said, "Okay, okay! I get it! In Chinese, we have an expression, 'Selling it as soon as you've bought it...'."

In other words, you have just learned about this, and now you are explaining it all to me as if you are the master of it.

I have not been able to find this expression anywhere since then. Perhaps it has been distorted by memory. What is the original Chinese expression?

Answer 1

The most common way you would say is

现学现卖 or 现炒现卖

However, the actual and original expression is

旋炒旋卖

if you read ancient Chinese novels. The character 旋 means right after. This expression is more correct, I would say.

However, you would just say 现学现卖 or 现炒现卖 nowadays, if you were to use the original expression, most likely people would not understand.