1. couldn't care less: not to care at all about something 根本不介意，不关心
The politicians are making a big deal out of the issue, but most voters couldn't care less.（政客们好好借题发挥了一番，但大部分选民对此根本不关心。）
Shelley couldn't care less about what other people thought of her.（别人怎么评论她，雪莉根本无所谓。）
To be perfectly honest with you, I couldn't care less whether he comes or not.（说真的，我根本不在乎他来不来。）
2. not give a damn: not to care at all about something, use this when you are very annoyed with someone or something根本不介意（一般很生气时才用这个词）
You're so selfish. You don’t give a damn about anyone except for yourself.（你太自私了。你只在乎你自己！）
not give a damn what/ who/ why...
I don't really give a damn what the press says.（出版社说什么我都不在乎！）
3. be past caring: to no longer care about something that you were worried about for a long time, because you realize that the situation cannot be changed表示“担心、介意都于事无补，于是就不担心、不介意了”
I used to worried a lot about my weight when I was young, but now I'm past caring.（我年轻时特别担心体重问题，但现在我一点不担心了。）
The company wrote and apologized for their mistake, but by then Sarah was past caring.（公司书面道歉了，但那会儿莎拉已经不介意这件事了。）
4. Who cares? 那又怎样！
So your house isn't perfectly clean. Who cares? （就算你家没有非常非常干净，那又怎样！）
5. So what? 那又怎样！
''Tom was really angry when he heard what you had done.'' ''So what? It's none of his business.''
6. What do I care? 那又怎样！
''He says he's depressed and really short of money.'' ''What do I care? It’s his own fault.''
7. Let him/ her/ them (do something): say this when you do not care if someone does what they have threatened to do表示说话人已经无所畏惧了
''Jenny says she's going to quit unless we give her a raise.'' ''Let her quit then. It's not as if we can't find another nanny.''
''They're threatening to disconnect the phone unless we pay the bill.'' ''Let them.''
8. tough: say this when someone tells you about a problem they have and you do not have any sympathy for them, especially because you feel angry with them 表示“某人向说话人哭诉，但说话人心里有气、毫不同情”：我才不管；懒得理你
''Mom, I don't want to go to school today.'' ''Tough! You're going anyway.''
''Can't we stop? I’m hungry.'' ''That's tough. I told you to eat something before we left the house.''
9. It makes no difference/It doesn't make any difference: say this when you think something is not important enough to affect what happens or change what someone decides无关紧要
''Do you want cash or a check?'' ''It doesn't make any difference.''
You can have a single room or a double. It makes no difference to the price.（双人间、单人间价格一样，你要哪个都行。）