I used to post regularly on the TES forum, which had thousands of regulars from the education world. I had to go cold turkey eventually as I was wasting far too much time on there. As Absent says, you got to know the usual crew and know which posts you'd enjoy, which would make you laugh, which would inform you, which to ignore, etc.
The ones that always disturbed me were the bullies, of which there were several, and some of whom had a hardcore following of hangers-on applauding their every nasty remark. You had to wonder if they behaved like this on a forum, how exactly did they behave in the real world with children in their care? On the other hand, you also had to wonder about some of the delicate blossoms who shrivelled up at a mildly sarky remark directed at them - how on earth did they survive in the classroom?
I've only been on Gransnet a few months, but haven't come across anything like the bullies/victims on the TES site - perhaps we've all both mellowed and toughened up in our old age!