Why did the cops laugh at Rod Williams' complaint?

Because the scenario explained was over the top and totally unbelievable. White people capturing black people so that they can take over their mind using hypnosis so that they can then use them as sex slaves.... How should one take it seriously... Also, the role of that character mainly is comedic relief.

First of all, that scene was probably the worst in a decent movie. It seemed like a forced comedic bit in an otherwise decent thriller.

As to why they didn't take him seriously, it was probably because the complaint sounded ridiculous. Black people being hypnotized and kidnapped by rich white people? I don't think I'd believe it either.