"Judge not lest you be judged. You therefore have no right to judge me when it comes to my sins!"
The world often takes this verse out of context and uses it to accuse Christians of being "judgmental" when they speak of sin. In the context of the verse Jesus is telling His disciples not to judge one another, something the Bible condemns (Romans 14:10; James 4:11). In Luke 6:41,42 He speaks of seeing a speck in a brother’s eye. In John 7:24 He said, "Judge not according to the appearance, but judge righteous judgment."
If someone steals, lies, commits adultery or murder, etc., the Christian can make a (righteous) moral judgment and say that the actions were morally wrong, and that these sins will have eternal consequences. Chuck Colson said, "True tolerance is not a total lack of judgment. It’s knowing what should be tolerated—and refusing to tolerate that which shouldn’t."
(More at The Evidence Bible)