social cropdusting

When someone walks into a room and seeds an argument over an intentionally dividing subject, and gets everyone upset with each other, and then casually leaves as the arguments continue to brew.

A group of close co-workers and I were having lunch in the cafeteria, when out of nowhere, Karen from accounting walks through and says "It's perfectly natural for Tom Brady to kiss his son on the lips.". Moments later, the anger and arguments between everyone defending their points of view had escalated to a point where nobody even noticed Karen had already left. Karen is a master at social cropdusting; she does it all the time. Karen is a bitch.