This is a (modified) translation of an existing joke which doesn't seem to be available in English.
Mandy owns a bar in Berlin Kreuzberg. One day, to increase revenue, she decides to allow customers to order drinks without paying immediately. Denizens in Kreuzberg hear about this and more and more customers visit Mandy's bar. Since they don't need to worry about paying, Mandy can raise prices and dramatically increases her revenue. The young and dynamic consultant of a local bank notices Mandy's success and offers her a credit line to ensure her liquidity. He is not concerned about getting the money back because he has the debt of the customers as collateral.
A group of investment bankers hears about the successful local bank and they transform Mandy's credit into collateralized debt obligations called ALCBOND(R), PUKBOND(R) and GUZBOND(R). These papers are generally referred to as SMA (Super Mega Asset) and are insured with the help of an Uzbek online-insurance company via email.
Since they are insured and are based on a very successful business, several rating agencies attest very good credit ratings. Nobody understands what the SMA papers actually are but due to the soaring market value institutional investors love SMAs. In the next few years, managing directors and investment specialists receive several hundred millions worth of bonus payments.
One day, the prices are still rising, a risk specialist has a look at the papers. He advises to demand payment from a small part of Mandy's customers. He is soon fired for his negative attitude which is not compatible with the corporate image. However, to prove that the risk specialist was wrong the management of "SMA International" decides to ask for payment on just a tiny slice of Mandy's customers. Surprisingly they can't pay as their debts equal a multitude of their annual incomes. With the help of external consultants several investigations are launched but it turns out that almost none of Mandy's customers can pay. Mandy goes bankrupt. ALCBOND(R) and PUKBOND(R) lose 95% value. GUZBOND(R), which was generally considered a boring investment, retains 20%.
Since the fast growth and general success of Mandy were well known, many of Mandy's suppliers had granted her very generous terms of payment. Additionally, they had invested in SMAs, too. Since Mandy can't pay and since the SMAs are worthless, most of the suppliers go bankrupt. With the help of the government the rest is taken over by a private equity investor who promises to restructure the companies and make them profitable again. The local bank is rescued by tax payer money. The CEO of the bank agrees to pass on his bonus for the last year.