what is this

when i went to post in a thread
below the post box, near options it has a dice roll thing

in one post i did it, and then hendo, who was offline, came up with a message saying i have rolled the death dice

what are they
he was offline and posted the moment of it, as if it was computer generated

what did i do??????

I dont really know what it was, just a random something I turned on, its gone now the dice wont trouble you no more.