Umm are you talking about in general or for a specific country?? There are different social and cultural norms in every country, but in my country (America) I would have to say surefire ways to get fired are:
- Using inappropriate language on the job
- Mixing too much personal with the professional (like talking about your sex life in the office, for example haha). In America it is generally considered very inappropriate to mix your personal life with your professional life.
- Harassment of another coworker, whether it be verbal or sexual ... basically don't try and date a coworker unless the feelings are definitely mutual haha: they could misinterpret your advances as sexual harassment
- Being openly racist at work or expressing hateful opinions against a specific group
- Taking too many breaks: America is a culture centered around WORK WORK WORK ... AND WORK SOME MORE haha. Most employers will not be happy if they find out you've been sneaking in some extra breaks.
- Don't be late too much ... American employers are big about showing up to work on time
- If you're LGBT (lesbian, gay, bisexual or transgendered) you need to be careful about how open you are in the workplace depending on the company's Equal Opportunity rules ... there are always stories in the news about LGBT people who've been fired from their jobs for simply being truthful about who they are. Just be careful.
This is all depends though too on the job you have: if the working environment is a bit more relaxed and/or liberal, some of these might not apply. It all comes down to your judgement on what would be appropriate or not in your specific working environment. Hope this helps!