Originally Posted by saudade
RP, in my head I actually have the big idea I think you're getting at sorted into a few different categories.
Yeah, I think RedPepper is conflating at least a couple of different behaviours here.
The person who comes into a group and acts badly enough that they start disrupting other peoples' relationships is typically just someone with, well, bad behaviour and relationship skills. People shouldn't date this person! Ideally, we don't want to date people who aren't savvy enough to spot this for what it is, either.
The cowboy/girl thing is something different, though. I don't think that there are very many people out there who have consciously decided to adopt it as a dating strategy (that would be pretty weird). But it is not that uncommon for someone with a preference for monogamy to meet someone who is in a poly- relationship, come to the conclusion that this person is "available", get emotionally entangled, and then start working to create the relationship that they want (a mono- one).
This isn't going to work if the poly- person is actually committed to, or really only ever wants to do, poly-relationships. But that's not true of every person in a poly- relationship, and there's a lot of cultural baggage that encourages people to pair off exclusively with someone when things get serious.
Obviously, either kind of person can create a lot of drama and unpleasantness. But the cowboy/girl thing is about someone trying to get the relationship that they want, not just about behaving badly.