I use to ran a 10,000 members forum and I have to say this is completely inevitable in any forums. We do expect immature people to be around us and some may just want to voice themselves in a bad manner to other users. There isn't really a way to stop it, but it's definitely something that damages the entire experience. Just wait till they grow up, got bored of doing it. But eventually another stray will just come around and continue where the others may have left off.
Yeah, there will always be the immature brats who don't have anything better to do or contribute. It will always happen in a popular forum. Eventually, I believe, the amount of immaturity goes down, but only after reaching an all time high, which is why places like TA need quite a few mods right at this moment. Eventually anyone who stays through the bad will be able to have a good conversation without blatant disagreement for the sake of disagreement.