L-2：laugh up one's sleeves 偷偷地笑

　　A:What's wrong with your face?

　　A:你的脸怎么了?

　　B:My brother did it.

　　B:我哥打的。

　　A:Why?

　　A：他为什么打你?

　　B:I laughed up my sleeves at him. He's seen his girlfriend off at the airport and had lipstick on his face and didn't know it.

　　B：我偷偷笑话他来着，因为他刚去机场送他女朋友，脸上留下了口红印，他还不知道。