I work for one of the largest smartphone manufacturers in the world. Our new device will be launched at the end of the year. We have already started selling pre-orders, and over 200,000 orders have been placed. There’s just one problem… the supplier of a main component is having trouble with his production. If he can’t deliver the component soon, the shit will really hit the fan (die Kacke am dampfen) on launch day.
This rather vulgar idiom, with its image of what happens when shit is thrown into an electric fan, is used to describe the results of a problem becoming public in an explosive way. It has been in use since the 1930s.