A currency disappearing in value and hyperinflation as a result. Not surprisingly, people don't like it very much when they go to sleep with their money being worth one amount and then wake up the next morning to find their money worth a lot less.

New York Times:

The first outbreak of public anger over Iran's collapsing currency and other economic maladies jolted the heart of the capital on Wednesday, with the riot police violently clamping down on black-market money changers, hundreds of citizens marching to demand relief and merchants in the sprawling bazaar closing their shops in protest.

Iran's official news media said an unspecified number of people, including two Europeans, had been arrested in the turmoil, which was documented in news photographs, at least two verifiable videos uploaded on YouTube and witness accounts.

Economists and political analysts in Iran and abroad said the anger reflected the accumulated impact of harsh Western economic sanctions over Iran's disputed nuclear program, as well as the government's inability to manage an increasingly acute economic crisis.

It came a day after Iran's president, Mahmoud Ahmadinejad, said at a televised news conference that the plunge in the value of Iran's currency, the rial - which has fallen by 40 percent against the dollar this past week - was orchestrated by ruthless currency speculators, the United States and other unspecified internal enemies of Iran. He urged people to stop selling their rials for dollars, a currency he once characterized as "a worthless piece of paper," and warned that speculators faced arrest and punishment.

How bad is inflation? Cato:

Since the U.S. and E.U. first enacted sanctions against Iran, in 2010, the value of the Iranian rial (IRR) has plummeted, imposing untold misery on the Iranian people. When a currency collapses, you can be certain that other economic metrics are moving in a negative direction, too. Indeed, using new data from Iran's foreign-exchange black market, I estimate that Iran's monthly inflation rate has reached 69.6%. With a monthly inflation rate this high (over 50%), Iran is undoubtedly experiencing hyperinflation.

When President Obama signed the Comprehensive Iran Sanctions, Accountability, and Divestment Act, in July 2010, the official Iranian rial-U.S. dollar exchange rate was very close to the black-market rate. But, as the accompanying chart shows, the official and black-market rates have increasingly diverged since July 2010. This decline began to accelerate last month, when Iranians witnessed a dramatic 9.65% drop in the value of the rial, over the course of a single weekend (8-10 September 2012). The free-fall has continued since then. On 2 October 2012, the black-market exchange rate reached 35,000 IRR/USD - a rate which reflects a 65% decline in the rial, relative to the U.S. dollar.

Ahmadinejad is getting the blame for all this. Not because of the nuclear program but because he obviously has a worse grasp of economic matters than even Barack Obama. In fact, my guess is there isn't anyone in Iran who understands what's happening which means it will almost certainly get worse.

The regime still has the guns - unless the army turns those guns on regime leaders. Iran as a more secular military dictatorship would still present enormous problems but might be preferable to the fanatical religious nuts who rule Iran at present.