Do Christians have to always be nice and polite about things?

Many people tend to think that if you are blunt with others and do not take their feelings into consideration then you are not a good Christian.  However, God has used people like this throughout time and even mentions many of them in the Bible itself.  Peter was stubborn, blunt, and would not compromise on what he thought was right.  Paul was the same way (2 Corinthians 11:6).  Elijah sat there and mocked the prophets of Baal at Mount Carmel (1 Kings 18:27).  It is not every Christians job to be this way; God has certain people with this personality and uses them to His advantage.  We need to make sure we look at the content of what people are saying and not always exactly how they say it.