So this happened last night while our team was waiting for Baron to spawn … it was a Coop vs AI match and we were way ahead, but Jinx needed our team to kill Baron to complete a mission, so we all went over to the river to wait for him to show up. Someone started dancing, and everyone there joined in. It was quite hilarious, because it went on for at least a minute.
Side note: I had no idea that Shelly (aka the Rift Herald) could dance too! But apparently she will join in if a champion starts dancing near her! (I looked it up afterwards to be sure!)