Firstly, "crap" is a rude word, and it means "shit". Here it means "rubbish". The rubbish can be anything, something untrue, something stupid. You want to say this to Nettenyahu?

Of course it is impolite - you are telling someone that they are talking nonsense or lying !! However it is OK to use it informally, perhaps with a little smile to avoid the slap.

Knowing the exact meaning and that it is offensive, I prefer OR try to avoid using it even if I lost temper:) It is easier to use these words in English rather than my mother tongue. I don't know why they sound horrible in Arabic! So, Marc, I can use it with you? Hmmm...NO! I know you have tons of similar phrases:))

You can say it to me any time. But I am Dutch. We are very direct. (In general of course, persons always differ.) So direct others find us impolite. And we have a very flat culture in companies. For me, the manager is not a 'better person' than the girl from administration. If my manager talks crap, I tell him: you are saying crap. I even told the CEO (big chief, many feathers) he was talking nonsense once. But, may-be I am a little cheeky, because I am technically that brilliant they won't fire me anyway.

:)))) Thanks, David:)