1. when a situation suddenly becomes difficult, chaotic, or dangerous
Professional
Social
when he/she heard the bad news, the shit hit the fan
This is a highly informal and vulgar expression, so we wouldn't advise using it around people who you don't know very well or with whom you wouldn't normally have frank and informal conversations. The idea is that the 'shit' is the trouble that will arise from a circumstance, and when it 'hits the fan', it will go everywhere, meaning that the trouble will become known and widespread.