Originally posted by: Rastus
Definately call the cops on him. It will give you a paper trail and also the cops will give you advice on how to proceed from here. If he's not on the lease, they also might make him leave or charge him with criminal trespass. You might also be able to file a small claims suit to try to get money from him.
Not going to happen, unless there is a domestic dispute going on and they make him leave to keep the peace (or he has crack in his pocket

)
There are laws to prevent roommates and landlords from suddenly deciding to throw people onto the street, lease or not. If he has physical possession of the property (his stuff's there, history of paying at least some bills, someone who will admit to the cops that he had a verbal if not written arrangement to stay there) than you have to legally evict him through the courts.
I've been a landlord for many years. Our procedure was to give tenants a 1 year lease that reverts to a month to month agreement after the year is up. And I believe any verbal agreement ("yes you can live here for $xxx a month") is treated as a month to month lease (could be wrong).
They could leave at any time, and I could ask them to leave at any time. I still had to give 30 days written notice by law, and after 30 days if they wouldn't leave I would have to start eviction proceedings, wait for the court date, and then come back with the sheriff. That's the law in Maryland, NYC isn't going to be all that different.