1.Inside joke,知情人了解的笑话

Mom, forget it. You’ll never understand it. It’s an inside joke.

We're not going to tell you what we’re talking about. It’s an inside joke.

2. House rules,行规

In this school there are certain house rules that everyone follows, but most important it that on one can cheat.

So, are there any other house rules in this office Ishould know about before I start working？

3. Cardinal sin,最大的罪恶

I’m sorry, Duran, but I didn’t know that driving your car without permission was suah a cardinal sin.

It’s not like it was a cardinal sin to kiss her! Yes, I have a girlfriend, but we’re not very serious.