Pain: P-A-I-N,名詞，痛苦，苦惱；ass： 屁股；

In English：someone or something that bothers you very much, but it's hard or inappropriate to put them on the table to talk about because of the bother-maker's identity. 某人或者某件事情使得你很煩惱，但是又不能放在臺面上說。

來源：

When your ass pains, it’s difficult for you to sit and sleep. 試想一下，當一個人的屁股疼的時候，他就很難去坐下來或者入睡。it will always bother you when the pain disappears. 直到痛消失后才不會再煩惱。Sometimes you can say ”pain the butt ” instead of “pain in the ass”

舉例：

For a short guy, sparring or fighting against someone with a height and reaching advantage can be a real pain in the ass.

對于一個小個子來講，和比自己長的高的人打架并且占優勢真的是很難的事情；

Getting all this spam email is such a pain in the ass. I wish they wouldn't send the damn stuff.

來處理這些垃圾郵件真的很煩，我希望他們不要再給我發這個爛東西了。