1. The grass is always greener on the other side。
这山望着那山高（不满足啊，不满足！）
I know it it seems like a good idea now but the grass isn't always greener on the other side, you should think about it some-more before you decide.
我觉得这个主意听起来不错，不过也许还有更好的，在你做最终决定前，你可以再想一下。

2. beef
互相抱怨，发牢骚
They've got beef.
他们闹矛盾了。

3. champ at the bit
等不及了
He was champing at the bit to go to the party.
他等不及去party玩了。

4. go gaga
疯疯癫癫
I went gaga when I saw my favorite band the other night.
那晚看到我喜欢的乐队，我“疯”了。（die for metal !!! ）

5. an eager beaver
形容人“迫不及待”
Calm down, don't be such an eager beaver, we're about to leave now!
嘿，别着急，别那么迫不及待，我们马上就出发了！

6. go back on one's words
说话不算数
If you agreed to meet a friend but then told them you were busy, you are going back on your word.
如果你答应了去跟朋友见面，但你又以“忙”为理由放了鸽子，那么你就是说话不算数了。

7. bite the hand that feeds you
恩将仇报
Don't bite the hand that feeds you, they might fire you!
别恩将仇报，他们可能会炒你鱿鱼。（对，我的心里只有工作）

8. not have the heart to do
不忍心
I'd tell my mum I really don't like her soups and they aren't very good, but I just don't have the heart too!
我好想告诉我妈，她做的汤不太好喝，我不喜欢。但，我就是不忍心。