In your opinion, what are the subjects that we mustn't ever discuss in an office?

In a perfect world, only professional items to be discussed at work.

In reality, this does not happen.  How can it?  If you live in a culture where religious holidays impact on social activities it will be discussed at work.  

Let's be honest, sometimes it is not the expats who instigate talk not related to work.  Many nationals are curious about certain cultures, behaviors and customs and when asked discussions are held on non-professional topics.  Women tend to hold discussions on fashions, hair and make up, shopping. Men tend to talk about cars, gadgets.  If bitesized discussions held can be ok, but if it starts to impact on the production of work then this needs to be looked at. 

Political

Personal Life

Religion

Staying away from discussing the following topics will make your work life a lot easier.

1. 1. 1. Religion

      2. Politics

      3. Your Sex Life

      4. Problems With Your Spouse, Your Children, or Your Parents

      5. Your Career Aspirations

      6. Your Health Problems

Personal issues that are considered a waste of time.Also , we shouldn't discuss our work together unless we were one team.

I personally don't like to discuss private matters at work at all, unless in explanatory sense to the right people, if they have a direct effect on my work or presence.

Other than that, I think it's ok to talk about any topic as long it remains within the commonsensible rules of respect & tolerance.

All topics can be discuss in a work place. But as much as possible, avoid discussing about personal life, politics and religions to avoid conflict.

Personal life

any subject out of duties clue, which will weast the valued time of work.

All the matters which do not relates to professional life, shoud not be discussed