1. In retrospect, that was clue number two.
回想起来，那是第二条线索。

in retrospect
回想过去，回想起来

e.g: In retrospect, I wonder if we should have done more.
回想起来，我想我们是否应该做得更多。

2. Doesn't concern you.
跟你无关。

这里concern相当于about。

e.g: This study concerns couples' expectations of marriage.
这个研究是关于夫妻对婚姻的期待的。

3. Don't get cocky.
别翘尾巴。

cocky
骄傲，自大，一般很让人讨厌

e.g: He's a cocky little man and I don't like him.
他是一个自大的小男人我不喜欢他。

4. OK, let me get this straight.
好，让我理下思路。

get sth. straight
理清思路，了解事实，搞清楚

e.g: I wanted to get the facts straight.
我想弄清事实。