If you've never played it, it's basically one person makes a wish and the next person to post is supposed to corrupt the wish somehow and then leave their own wish.
Here's an example:
Poster A: I wish for a bag of infinite buttons. Poster B: Wish granted, but the bag suddenly developed a taste for human flesh and ate you. I wish for a lollipop. Poster C: Wish granted, but the lollipop comes in the worst flavor possible.......paint red. I wish for a pony.