The first thing it depends on is where you live. The US has no law requiring niceness, but perhaps niceness-enforcement exists somewhere in the world. The second thing it depends on is exactly what he does, where and how. If he comes into people's houses uninvited and starts harassing them, that is generally a crime. If he makes nasty remarks to people walking down the street, you can't even sue him.
If the person commits in a crime, you can report him anonymously. However, for there to be any prosecution, someone will have to testify in court: anonymous criminal testimony is inadmissible in the US. If there is no crime, just a potential civil action, the part would hire an attorney to file a complaint, etc. and that party would be named (not anonymous), would have to testify, and would also have to have been harmed. The police will not get involved in a civil dispute. Based just on what you have said here, your attorney would very likely say that there is no case to be pursued, and your only solution is to ignore him.