UAL 2499 (EWR-SFO) diverted to ORD on 10/21/2023 due to a lavatory that was so bad that it was deemed a biohazard.
According to a passenger on the flight, the bathroom apparently looked like something out of the movie The Exorcist. In Chicago, a crew of 4 came onboard for about an hour to clean up the bathroom. Then, the flight continued on to San Francisco without incident.
That's one expensive trip to the bathroom -- the diversion probably cost 5 figures...
https://www.flightaware.com/live/flight/UAL2499/history/20231022/0120Z/KEWR/KSFO