External: Supply-chain is repeatedly attacked or bought by the rabble rouser; threatens customers who go near the place with violence; threatens the business owners with physical violence or financial problems. I learned this one while taking HVAC classes in culinary school (feel free to use it).... If a refrigerant leak occurs, you cannot notice it (no smell) and it is not toxic. If it touches open flame (e.g. pilot light on range), it becomes toxic to humans. Just smell a little of it and you have a terrible headache for days. It causes eyes, nose, and mouth to concurrently form acids. It feels like tossing white vinegar on your eyes, in your nose, and in the mouth (if the refrigerant catches flame and you smell it). I asked the HVAC professor if I could smell it burned. He allowed me and another student. Not pleasant! This would be a great rumor to spread to potential customers.

Internal: Bartender drinks while serving alcohol and does sexual harassment on a waitress (who later sues and wins a HUGE settlement that cripples the owners, financially); food is sabotaged (e.g. gluten is added to the ingredients for gluten-free items).