be mad at 對…憤怒
I'll be mad at you if you do.
你再這樣，我可要生氣了。
If I return empty-handed, my brother'll be mad at me.
如果我空手回去，我哥會對我發火的。

on purpose 并非偶然地; 故意地; 特地; 特有的目的
Have you discovered that your friend gave you bad advice on purpose?
你曾發現你的朋友故意給你提壞意見嗎？
Usually people aren't trying to hurt your feelings or upset you on purpose.
通常，人們都不會故意試圖去傷害你的情感，或者惹怒你。

least of all 最不， 尤其;
I'm gonna miss you least of all.
不過我還是會想你們大家的
But no one, least of all afghans, expects states to actively work against their own strategic interests.
但是沒有人，至少所有阿富汗人，會認為各國會積極去做一些違反他們自己戰略利益的事。