Maybe you should read some of the other verses where we are commanded to judge, especially judging public teaching about Christ. It also says not many of you should presume to be teachers... does that mean none of us are called to be teachers? I'm certainly willing to be judged by the sword I weild. It's the only way to go.
We are not to judge one's spiritual condition (we might make speculation but that's all it is), whether one is saved or not, without any admission one way or the other by the person in question. However, we are commanded to judge (e.g. make judgements on or discern) truth and error in what is being taught in the name of Christ. So don't try the prooftexting thing with us.
So far, all I have seen are the pineapples on Warren's shirts.