Nouriel Roubini was in fine form yesterday, scaring the bejeezus out of his followers on Twitter by saying that several huge financial institutions could collapse in the blink of an eye like MF Global.

These houses of cards, Roubini tweeted, include:

The problem, as Roubini has consistently warned, is the banks' dependence on short-term financing to maintain their long-term asset leverage and run their businesses.

What killed MF Global, Lehman Brothers, Bear Stearns, AIG, and other huge financial firms, after all, was the sudden refusal of short-term lenders to continue lending money to the firms.

Every day, the big Wall Street firms borrow tens of billions of dollars in low-cost short-term loans. They then use this money to make long-term bets on assets that yield more than the money costs to borrow. And then they happily keep the difference between the two.

In good times, the banks come to take this funding for granted: They just keep rolling over their huge debts every day, repaying the old loans with the money from new ones.

When the overnight lenders suddenly get suspicious and the money disappears, however, it's as if the oxygen is suddenly sucked out of the room.

In additional tweets, Roubini argued that JP Morgan and Citigroup were actually less at risk because more of their funding comes from insured deposits. So that's some good news for you. Dan Freed of TheStreet has more on Roubini's tweeting.

If you don't understand this short-term funding dynamic, and the enormous risks it creates, read this excellent William Cohan article on how Jon Corzine just flew MF Global into a mountain.