It's a fine line which you will have to determine at the time.
"He stood in the doorway, and we just looked at each other for a while." -Does not justify deadly force.
"He stood in the doorway, and said if I tried to leave he would kill me." -Justifies deadly force in most states. See the difference? At the time of the event, you must be able to articulate that you were in fear for your life, or of serious bodily injury. "He was standing in the doorway so I shot him" doesn't cut it.
And I don't escalate force. It's deadly force or I walk away. I gave up shoving matches and violent horseplay when I started carrying a gun.
Not to nitpick, but to kind of think out loud for my own understanding.
I don't agree that your second situation ("He stood in the doorway, and said if I tried to leave he would kill me") necessarily justifies deadly force, either. We all agree that deadly force may be used in self-defense to prevent death or grave bodily injury. This situation doesn't rise to that level, not yet, anyway. In order to be able to justify using deadly force such as your pistol, you must be able to explain why the guy in the doorway had the ability, the opportunity, and intended to put you in jeopardy (AOJ for ability, opportunity, and jeopardy). Him saying that in a menacing way (in such a way a reasonable person, ie a juror, would not think he was joking) meets the jeopardy requirement. But what about ability and opportunity? That's where you need to explain what kind of a weapon, or disparity of force, he threatened to use against you. If he's within 21 feet or so of you, then he has the opportunity to present a grave threat even with his bare hands or with a contact weapon. So jeopardy and opportunity could be present.
Ability though? What is his weapon? How did you know he had one? It's ok if he told you he had something in his pocket, that counts. Just an unspecified unease with his appearance or manner though doesn't necessarily cut it though, when it comes to explaining to the police and the prosecutor charging you with manslaughter what kind of deadly threat the guy in the doorway was. He could be unarmed and still have the ability to be a deadly threat, if somehow you knew at the time that he was an ex-commando or bare-handed killer of men. But unless you can explain that, or show that he outweighed you significantly and maybe you have a signigicant medical disability issue, you will have a difficult time claiming disparity of force one on one versus the guy in the doorway talking crap. If you want to have a hope of not getting mangled by our own criminal justice system, you need to be able to explain this AOJ thing in your situation in terms that someone who wasn't there can comprehend.
(Plug for a training class) I would not have been able to explain that until after I took one of Massad Ayoob's 40 hour classes, though. I'd heard AOJ mentioned once or twice in other classes, but it took me some more advanced CCW class training before I could apply it somewhat.