Here's how it works:
the poster has to make a wish,
the next poster has to grant it, but something goes horribly wrong
(Ex: i wish i was a bunny. Next poster: OK, you are a bunny, but you die of bunny sickness)
The poster then makes his own wish, and the poster after THEM does as above, and so on.
I'll go first: I wish I had a Wii.