Acts 23:2-5 (NIV)
At this the high priest Ananias ordered those standing near Paul to strike him on the mouth. Then Paul said to him, "God will strike you, you whitewashed wall! You sit there to judge me according to the law, yet you yourself violate the law by commanding that I be struck!"
Those who were standing near Paul said, "You dare to insult God's high priest?"
Paul replied, "Brothers, I did not realize that he was the high priest; for it is written: 'Do not speak evil about the ruler of your people.'"
Paul had got himself into a real pickle of a situation when he insisted on going back to Jerusalem against the advice of many of his friends (but led by God). Ever the fearless one, Paul upset a lot of people with his speech and ended up on trial before the Sanhedrin. Paul, knowing the law well, lashes back in anger at the one who ordered him to be struck. Evidently, Paul did not recognize who the high priest was. Perhaps this is a bit of corroborative evidence that Paul had a problem with his eyesight. Regardless, Paul is rebuked for insulting the high priest and humbles himself to apologize, quoting from scripture to show why it was inappropriate on his part.
We see this theme having respect for authorities repeated many times in the New Testament. But here we see that this respect is due even when the authorities are acting wrongly. Even a slave is to honor his master when it clear that the institution of slavery cannot be condoned. God has instituted governments and families in this world to provide order. We can speak the truth, but it must be done with respect and in the proper manner.
Romans 13:1-2 (NIV)
Everyone must submit himself to the governing authorities, for there is no authority except that which God has established. The authorities that exist have been established by God. Consequently, he who rebels against the authority is rebelling against what God has instituted, and those who do so will bring judgment on themselves.