No hard feelings.
别见怪！不计前嫌了！
I'm sorry that things ended this way. But no hard feelings right?
很遗憾最后事情变成了这样，但是，没关系的对吧？
hard feelings refers to anger between people because of something that has happened
hard feelings 就表示由于发生了某些事情产生了芥蒂，结下了仇怨。
The argument caused a lot of hard feelings, but finally we got over it.
那一次吵架让我们关系紧张了一阵，但是我们后来还是解决了。

Get a life!
telling someone to fix themselves or saying that they spend too much time on trivial matters. or saying this to a boring person when you want them to do more exciting things.
过真正有意义的人生吧。别虚度荒废了，别每天把时间都花在鸡毛蒜皮毫无意义的小事上面了。
Don't tell me you're cleaning the house on a Friday night? Get a life!
别告诉我你在星期五的晚上搞卫生噢！？？！能不能做点刺激的事情？
You guys should just stop moaning and get a life!
别叽歪了！做点儿有意义的事情吧！

Say When!
什么时候好了说一声！（经常用在倒饮料酒水的时候）
- Say when.
- When. / That's enough. / OK.

Sometimes I'm not the sharpest tool in the shed.
I'm not the brightest candle on the cake.
I'm not the brightest bulb in the box.
我有时候有点傻。我有时候不太聪明。

I'll say.
Tell me about it.
You can say that again.
我非常同意。可不是么！

Where were we?
Where was I?
我们刚刚说到哪里啦?

talk one's ear off
唠叨，喋喋不休，说个没完。
Stay away from Hanna. He will talk your ear off if he gets a chance.
离Hanna远一点。他一有机会就唠叨你。

You don't want to do sth.
警告你别去做某事