If you look at this question, you will notice that every answer except the 'best-answer' got a downvote from this guy. And his comments are particularly annoying - he makes it clear this was deliberate and had nothing to do with the validity of the answers.
What really troubles me is that the 'best-answer' is COMPLETELY WRONG AND DANGEROUS and somehow got some upvotes.
Update: Okay, I need to clarify a few things. First off, I was a little too hasty to accuse The Rook and Longpoke of being trolls. At first I thought they were intentionally trying to create trouble - I didn't think they were actually serious. In light of this, I think downvoting instead of a suspension is in order.
However, having said that - anyone who posts the following comment:
-1 to every answer except this
...and proceeds to downvote the other answers without explanation - is a red flag.