W: Why? Peter? You look unhappy.
M: I lost my temper at an old man just now, and I feel badly.
W: Oh, you shouldn't have done that. But why did you get angry?
M: Lack of patience. He was counting out the coins, one by one, with his fumbling fingers. I was filled with exasperation at the checkout point. Finally, I said to him, "Can' t you count a bit faster? I was very busy". He flushed. Suddenly it occurred to me I was very cruel and impolite. Because he is rather old and he can't help it and one day I will become old myself.
W: Did you apology to him?
M: Certainly, I did. But I still worry my lacking of patience. And I am dying to find a way to become more patient. Because when you are impatient you may become rude and hurt somebody unconsciously.
W: Yes, I also have such a shortcoming. Sometimes I shout sharply to someone slow to understand. We must find more means to calm ourselves in such situations, especially when we are under great pressure. I have found some books about this problem. There are some useful tips.
M: Please tell me some tips.
解析
Why did Peter look unhappy?
细节题。从对话中男士的话I lost my temper at an old man just now，and I feel badly．可知他心情不好是因为对一个老人发脾气了。因此，正确答案是D。