Nouriel Roubini got famous for predicting the housing crash, although his timing was a bit off. He started his housing doom predictions in summer of 2006 (when the S&P 500 was around 1200), and was vindicated by the crash.
Unfortunately he remained bearish throughout the subsequent recovery, and now that the S&P 500 has recovered to 1600, he finally decided that he likes stocks.
Quick! Sell everything!