My grandfather is nearly 90 and in his second childhood.
我祖父快90岁了，什么事都需要别人来做。

Nonsense, I don't think his painting is any better than yours.
胡说，我认为他的画比你好不到哪去。

I must not stay here and do nothing.　
我不能什么都不做待在这儿。

You don't want to do that.
你不应该去做。

The elevator girl reads between passengers.　
开电梯的姑娘在没有乘客时看书。

If my mother had known of it she'd have died a second time.　
要是我妈妈知道了，她会从棺材里爬起来。

If you think he is a good man, think again.　
如果你认为他是好人，那你就大错特错了。

That took his breath away. 　
他大惊失色。(很形象的说法啊~)

I won't do it to save my life.　
我死也不会做。

Work once and work twice.
一次得手，再次不愁。