A game of posting tag.

Once it starts, whenever people post anywhere, the "its" start to get seeded randomly (say 1/10 or 1/20 odds of getting it per post, etc). If you're "it", you attain some way to cause mayhem, such as being able to add some pre-selected options/doodads/edits to other peoples' posts (like reactions in discord etc only far, far worse).

There can only be one "it" per thread. However this is on a timer and doesn't last long (maybe 2 minutes), and you must refresh it by making a post, or you lose your "it" status and it'll be granted randomly to any new post in the thread. While you're it, the background changes for you, and the posting/quick reply box has a flashing timer to let you know how long you have.

However, when you're it and make your obligatory post to reset your timer, an indicator next to your name comes up, and when anyone clicks on it, they've tagged you, become it and you lost your it status. You can try to click on your own tag sign first to guarantee keeping it, but that might be near-impossible to re-pick it up yourself in a crowded thread, or simply barred by design so that it keeps moving.

All the idea boils down to, is a weapon of mass distraction.