He's waiting for you out there. And he can wait as long as it takes.
You know what you did; you fucked his girl. All he wants is to talk - at least, that's what he tells you. In reality, he's got a switchblade he'd like to use in slicing your stomach open.
From your room on the third floor, you see him, sitting on your stoop. He's not breaking any laws, not trespassing since he's friends with the building manager, never made any inflammatory comments to you. But you can't leave, and he knows this.
So, what do you do? You drop a brick on his head - except it misses. Now, he's got a reason to go after you. Now, you're wondering just how sturdy that fire escape is.