a pain in the ass可不是“屁股疼”，正确意思是“让人讨厌的人或事，讨厌鬼，烦心事”。

【例句】
They're a real pain in the ass, aren't they?
它们真是令人心烦，是不是？

He may be a superstar, but most parents consider him a pain in the ass.
他可以算是超级明星，但大多数家长觉得他很讨厌。