depends on your audience, around friends it would be okay to use a bit of casual talk or slang, for example, in english it would be okay to say phrases such as 'idiot' 'stupid' etc. Slang differs a bit around japan, for instance in Osaka, あほ aho is quite common. But if you were talking to people you don't know, people in your workplace, or important people such as your boss you would not use words like these, just like anywhere else in the world. As you might know, there is formal and informal speech in japanese. informal speech includes relaxed, casual speech and slang. some examples of slang or 'bad words' are: バカ あほ these are insults, meaning stupid. In Japan, it is considered rude to use informal languege to people you haven't met before, or people of higher status than you. Otherwise, there arent any particular phrases you should avoid, just use informal and formal speech according to your audience.

I don't understand your question well.