今天介绍的和laugh这个字有关的习惯用语不一定会使当事人高兴：To laugh up one's sleeve。Sleeve就是衣服袖子。To laugh up one's sleeve从字面上来看是在袖子里笑，实际上也就是偷偷地笑。To laugh up one's sleeve的真正意思就是偷偷地笑话某人，因为这个人有些可笑的地方，而他本人还没有发现。例如：

"We were all laughing up our sleeves at the teacher when he was up at the blackboard explaining the math problem. He had a rip in the back of his pants and didn't know it."

这句话翻成中文就是：“当老师在黑板前讲解数学题的时候，我们都偷偷地笑，因为他裤子后面有个裂缝，他自己还不知道。

其实，这种情况是经常发生的。下面又是一个例子：

"We were all laughing up our sleeves at our brother when he sat down at the dinner table. He'd seen his girl off at the airport and had lipstick on his face and didn't know it."

这个人说：“当我们的哥哥坐下吃晚饭的时候，我们都在偷偷地笑他，因为他刚去机场送他的女朋友，脸上留下了口红，他还不知道。

the top and bottom of it 真相；整个事情的原委