I've seen that before. Guy next to me constantly has his seat jostled by the guy behind him. This was after the jostler emptied an F bin to make room for his stuff and left the removed items in the aisle with no comment. The two bickered back and forth about the pushing on the seat for about half the flight. I was certain the confrontation would escalate. The FA's looked worried. I was watching like it was a soap opera. Very entertaining if not quite a bit uncomfortable as well.

Then suddenly it stopped and the two at odds strangers took out some paperwork and began talking business. They apparently work together and were putting on a show.