Buffet losing his ass, well his stockholder's asses. He sold roughly $4.5 billion in naked put options. So you understand, a put is a bet that the market will go down...IF YOU BUY ONE, but if you sell them you are fucked if the market goes down. This is an off the exchange deal so it may be that the put holders cannot just sell them, but anyway. BUT the law is that all options are marked to market at the close of business each day. This means Buffet has a margin call of around $6billion. Read the gory details HERE.
(Via Big Picture)