Perhaps I just come across a higher than average number of nasty cows but I find myself really quite shocked at the number of women that I come across that want to just divide and conquer and cause trouble (and yes, I know men do it too but I personally haven't come across any that do).
I am on a facebook group of other mums that gave birth at around the same time as me. The woman who runs the group is a typical 'divider and conquerer' and will often try to gang up on various group members if she doesn't like what they say, by sending facebook messages to other group members basically bitching about that member and trying to turn others against them. A few women have been bullied off the group by her. She seems to pick up on a perceived flaw of someone and then focuses on it and turns people against them by going on about it. It is a large group and I rarely post, I just keep myself to myself and don't get involved in it.
Then there is a mum at my DCs school that seems to really like stirring up trouble and turning people against others. She was best of buddies with one other mum, then they had a falling out of some kind, and she spent months bitching about this other mum and essentially trying to turn everyone against the poor woman. Again I kept totally out of it.
I've come across many other examples of that kind of behaviour in recent years too. It just shocks me really that grown adults can act in that way.