You'd better button your lip.
button one's lip 字面意思是：“用纽扣扣上嘴唇”，这个习语的真正意思当然不是如此，像多数习语一样，这是个比喻的说法，扣上嘴巴后嘴巴就不能张了，也就表示：“闭嘴，住口，保持沉默”。因此，当美国人说"You'd better button your lip."时，他/她要表达的意思就是:"You'd better shut up."、"It's wise for you to keep silent on this topic."。
Colleague: Excuse me, I can hardly grasp what you're talking about. What financing cost?
Boss: Oh, boy, you'd better button your lip if you are not quite familiar with this business.
①I agree to take actions to prevent the loss immediately.
②We should put more money into this project.
③Perhaps we should buy that company as soon as possible.
④It's none of your business.
button vt. 用纽扣扣上
Ferguson stood up and buttoned his coat.
It's very warm, he didn't even button his coat.
The young man slipped on the shirt and buttoned it up.