People who are terrible at arguing. No matter if they sided with the angels, I will refuse to be on their side if all they know how to do is be stubborn and nothing else.
Edit: more specifically the double posting rule is in place to stop multiple posts that should be one post. There are exceptions like:
1) Posts to bump threads because of some new event (e.g. this scenario)
2) Posts that have to be broken up in order not to break the forum (e.g posts quoting more than ten times)
3) Posts that are very long and discuss two different topics that would benefit from a logical split.
4) Reference-type posts and art threads where the artist can post one art per post in a row.
... Says Chekhov.