Supposedly he read online that WiFi signals are toxic, and has self-diagnosed as being sensitive to these "carcinogenic" waves, and accuses everyone around him of being insensitive to his special status. So the guy began to harass her AND the landlady of the building they both live in, insisting that the router be turned off. After doing a bit of tech tweaking, my friend made her home network and laptop invisible to other devices. This seemed to stop the problem temporarily.
However a month later she got a new cellphone and had to make the router visible again for a short time in order to set it up with the phone. Almost immediately the neighbour called the landlady to complain that the WiFi was being used as a weapon, AND then he called the police. Fortunately for my friend, the police believed her side of the story.
Fed up with all the harassment, she's taking the guy to court.
In the meantime, he continues his insanity by getting a funky gadget that can tell him where the WiFi signals are, and lying to the police about the situation. It has gotten to the point where the police are laughing about him because of his antics.
You can't make this stuff up, folks.