monkey 猴子，business 生意,买卖，monkey business 可不是猴子生意，引申为捉弄，恶作剧的意思。

【例句】
After the teacher left, there was a lot of monkey business in the class.
在老师离开后，班上恶作剧连连。

Stop the monkey business and get some new ones.
别再胡闹了，买些新的吧。