直接进入主题，crack a joke 是“开玩笑”的意思，善意的、有意思的玩笑。
举个例子
Every time Tom cracked a joke,
his buddies broke up laughing.
每次汤姆讲个笑话，他的伙伴们就大笑起来。
1. crack up
crack up 是什么意思？
（1）To laugh very hard，
or To cause someone to laugh very hard.
笑得厉害，或使某人大笑
举个例子
We all cracked up at Josh's joke.
听了乔希的笑话，我们都笑坏了。
Josh's joke cracked us all up.
乔希的笑话把我们都逗乐了。
（2）To experience a mental or emotional breakdown.
经历精神或情感上的崩溃
举个例子
All those days of sleep deprivation finally caused me to crack up.
那些天的睡眠不足终于使我崩溃了。
除了以上两个意思，crack up 还有“摧毁某物”的含义。
举个例子
He drove into a tree and cracked up his car.
他开车撞到一棵树上，把车撞坏了。
2. crack under
crack up 和 crack under the strain 几乎是同一个意思？
crack under the strain
to have a mental or emotional collapse because
of continued work or stress.
由于持续的工作或压力而精神或情绪崩溃。
举个例子
He worked 80-hour weeks for a month and finally cracked under the strain.
他连续一个月每周工作80个小时，
最后在压力下崩溃了。
3. crack a few eggs
you've got to crack a few eggs to make an omelet
（要做煎蛋卷，你得打几个鸡蛋）有失才有得
Sometimes, you have to do unpleasant things in order to complete，
a task or meet a goal.
有时候，为了完成一项任务或实现一个目标，
你不得不做一些不愉快的事情。
举个例子
Your students clearly don't respect you.
I know you don't want to yell at them,
but you've got to crack a few eggs to make an omelet.
你的学生显然不尊重你。
我知道你不想对他们大喊大叫，
但你得打几个鸡蛋才能做煎蛋卷。
4. the first crack at
try for the first time 用腻了？
试试 the first crack at (something)
“第一次尝试(某事)”
举个例子
I let them have the first crack at producing my film,
but they weren't interested,
so I took my script to another studio.
我让他们先试着制作我的电影，但他们不感兴趣，
所以我带着我的剧本去了另一家工作室。
5. crack a nut
如果某人 use a sledgehammer to crack a nut 用长柄大锤敲开坚果，
那代表“使用过度极端、过于复杂或不切实际手段或力量来完成相对较小或简单的事情”。
举个例子
The widespread campaign by the government to reduce childhood obesity is,
she says, using a sledgehammer to crack a nut.
她说，政府为减少儿童肥胖而开展的广泛运动，
就像用大锤砸坚果（用宰牛刀杀鸡）。
