I take it Ivon just moved into this place? On one hand, I can understand not wanting to rock the boat being a brand new resident. Of course, the neighbor sounds and acts like a real piece of work. Probably not much of a stretch to think that this guy isn't the type to just take a hint and move on. I'm thinking anyone who would do that over what sounds like absolutely nothing, most likely has some issues.
If there were more choices in the survey, one of them should have been to somehow let the guy know that Ivon wasn't going to stand for that type of behavior and was thinking about taking it further up the chain of command. That's where the services of a good doorman can mean so much to a resident. From that one, limited exchange, it's hard to tell if the doorman might be up to a little off the books relationship repair or not. If so, he should at least be able to find out what the reasoning or motive was that caused the neighbor to do what he did.
If Ivon can't get the doorman to do a little covert fact finding, he might as well call the cops. He's got nothing to lose and it doesn't sound like the neighbor is worth any type of mercy....