I don't know what a sack coat is, but I'm sure you'd look handsome in it.

我不知道什么是男便装上衣，但我相信你穿起来一定很帅。

I should wear evening attire or a sack coat.

我应该穿睡衣或男便装上衣。

That's how I know that if I ever have an audience at the Vatican, I should wear evening attire or a sack coat.

那本书说如果在梵蒂冈开会，我应该穿睡衣或男便装上衣。