I'm shocked and surprised.
Maybe there's a different word you guys are using for this concept, but I thought a Poly site would be rife with conversations about it.
Simply put, bringing someone else into a disagreement that one should be handling themselves.
Here's a story to explain it:
Person A has a disagreement or some trouble with Person B. Person B does something Person A doesn't like.
Person A does not (or cannot) resolve this with Person B, but instead approaches Person C to talk about their problem with Person B.
Sometimes Person A is hoping Person C will do or say something on their behalf, sometimes Person A is just looking for righteous justification about how wronged they feel in order to help quell the niggling feeling that they should really deal with the problem directly.
In this scenario, Person A is triangulating Person C into a problem that exists between Person A and Person B.
I once lived with my husband and my best friend in a house, for about three years.
My best friend was not involved sexually with either of us but I love her like a sister, and my husband was physically attracted to her and at one point had hoped she'd agree to Poly with us.
My husband and best friend grated against each other regularly - she is sarcastic and edgy and he never did figure out how to deal with it.
Early on when he'd talk to me about his problems with her, I would listen sympathetically and then try to help him find some ways to deal with her without getting to the point of feeling upset like he obviously was feeling.
Unfortunately, me trying to guide him to find his own solutions resulted in him getting mad at me, and then we'd fight. He figured since she was MY best friend that I should have a talk with her and get her to treat him with more respect, but he was never confident enough to come out and SAY that - he just pouted and gave me the silent treatment and stomped around the house for a few days.
(Note, all members of the household are over 25 at this point).
My (now ex-)husband and I had a number of stand-offs about this topic. I didn't believe it was my responsibility to teach others how to treat him, and he resented me for many years - even after our divorce.
I'd love to hear about your experiences with triangulation and how you dealt with them successfully.
In a way, I think getting divorced was a successful experience with standing up to triangulation (and other boundary issues), but now I'd like to attract a healthy, happy, respectful and responsible relationship (or three) and I'd love to hear success stories that didn't involve setting oneself free