"Trolls" and comment wars
If you think forums are bad you should try YouTube.
I've seen some of the most vile attacks waged in YouTube comments, peppered with profanity and names like "retard". It's unbelievable.
What gets me even more is that this happens in Christian videos by people who identify as "Christians".
There are several videos out there on controversial Christian topics like marriage in Heaven and universal salvation where these "comment wars" are particularly prevalent. Their language is from the gutter. You wouldn't expect it from people of faith.
Like Abraham Lincoln once said, "You can't believe everything you read on the Internet."