WHY

After he goes or tomorrow, let your neighbours know about the guy and that he's harassing you. And if said guy comes by again to help out with getting him to leave.

Odds are they will do something if the need arises. If they help, thank them with food.

Honey, you really need to call someone about this, even if it’s just the concierge, just let someone know

Can you call your mutual friend to speak to him?

Hmm