"Triangling" is a circumstance in which one person speaks to another about a third person in a negative way. It often creates closeness with one person at the sacrifice of the third person. To avoid this, try not to agree with the second person in saying or supporting negative statements about the third person. Encourage the speaker to take their concern to the third person directly. Let them know, if you can, that saying these negative statements makes you uncomfortable. The "Meeting in the parking lot" often has these elements.
Example
"I heard that Pat went and did something trivial on Sunday when you were presenting that workshop. You needed him there, not out playing hooky!"
De-triangling:
"What you're saying is true. He wasn't there, but it makes me feel we're putting him down when we speak this way. I'll have to think about how I feel about this and talk to him directly. You can do the same if it upset you."
Transforming Conflict Joanna Komoska