People who decide to grind their axe to a total stranger.
Story: I already belong to one Meetup crafting group. Looking to expand my knowledge base/network, I decided to join another in the same general area. When the organizer (Abe) introduced himself to me, he casually (I thought) asked if I belonged to any other groups. I mentioned the other group in the area. He immediately went into a loud tirade against that group's organizer (Bea) in front of other members and patrons of the restaurant. I had innocently stumbled upon an intense rivalry between these two groups. I made my excuses after an hour and left, never to return. I was so dismayed by his vitriol and wild accusations, that when I next attended my original group, I took Bea aside and told her of his accusations. She told me that he had tried to stage a "coup" of the original group, and when that failed, he started his own group and had been bad-mouthing her ever since.