can't boil an egg不是指“不会煮鸡蛋”，其正确的含义是根本不会做饭，不擅长做饭。

【例句】
We should eat something beforehand because my brother's making dinner, and he can't boil an egg.
我们应该事先吃点东西，因为我哥哥在做饭，而他却不擅长做饭。

My girlfriend can not boil an egg,she always orders a delivery when she lives alone.
我女朋友根本不会做饭，她一个人住的时候老是点外卖。