Walking in the San Francisco docks, I came across about 30 cats grouped together taking the sun on an upturned rowboat. Their expressions told me that if I stepped any closer, they would join in an attack that would leave me looking like a torn up rag doll.
Talking to a man working on his fishing boat, he said that they were feral, and at night would take care of rats and mice around the boats. They looked like they would also 'take care' of any human who crossed them.
The meanest looking critters I have ever seen.