Out of the loop

Imagine there's a big public square and everyone is encouraged to draw on it in with chalk of any color. Except you only get one tiny fragment of chalk every five minutes.

Hard to make anything meaningful, huh?

So people coordinate, usually via discord chat. Someone comes up with a pattern, maps it onto coordinates on this square, and users go out and put down their mark at preselected coordinates, and others mark on top of it, and the most coordinated communities succeed in creating and maintaining coherent images - which are usually ads for their own community. Or flags. Or anime characters. Or something else just as mind-numbingly boring.

Because it's difficult to maintain any real estate on this square with so many people throwing chalk everywhere, communities build robots to go make their chalk marks for them. You get your chalk piece and you give it to a bot and it goes out and puts it in the proper coordinates. Individuals can still make marks, but they usually only last a few moments before a bot or community horde of zombie people come by and place their marks over it.

And this boring nonsense goes on for a few days until the admins decide arbitrarily that the event is over.