I will show you the door.

(你以为是)我送你到门口。(I will show you to the door.)
(但其实是)我想请你滚蛋。(actually: I want to ask you to get away.)
这句英文原意是「大门就在那里」,有对着某人下逐客令的意思,是很不客气的说法。例:Be quiet, or I will show you the door.(安静,否则我会叫你滚出去。)

送客正解:I will show you to the door.或I will walk you out.

Were you out to lunch?

(你以为是)你出去吃午餐了吗?(Did you eat yet?)
(但其实是)你是疯了吗?(actually: Are you insane?)
out to lunch是一组俚语用法,意指疯狂或心不在焉,摆明是在教训别人。例:It seems that you were out to lunch in class.(你上课时似乎心不在焉。)

问别人吃饱没,正解:Did you eat yet?

I am a confidence man.

(你以为是)我是个有自信的人。(I am a confident man.)
(但其实是)我是个骗子。(actually: I am a cheater.)
confidence是自信、信任没错,但confidence man却是一组俚语用法,专指诈骗钱财的骗子或诈欺者。例:We finally realized that he was a confidence man.(最终我们发现他是个骗子。)

有自信的人正解:I am a confident man.