When you are talking and people look away in mid-sentence and start talking to somebody else, this is a bad sign. That happened for weeks in meetings I used to have at one job a while back, and I eventually got fired from that place too. Same thing is true for letters and emails. You'll be going along back and forth with someone and then - slam - they just stop answering, and there were still plenty of things to give and take on.
It takes me so long to warm up to a conversation, whether in person or privately, that when it just stops or gets clamped down or whatever - and it isn't over yet - I have a tendency to say "ok, I won't bother you any more." Because, if you really knew me you'd recognize that I'd rather not have engaged with you in the first place. I'm the kind of person who wants to go home, be home, and stay home. To go out and mingle is something I have to kind of prepare for. In many social settings I usually start out being the guy who waits and watches before jumping in.* So to finally get in on things only to watch the process of communication fumbled, just sort of reinforces my initial desire to have stayed in the background observing in the first place.
I find it's like that with people you talk to where you say "we should get together some time, go out to dinner or whatnot," and it ends there. I guess I'm the type of person who, when I hear that, thinks "ok, we're going to get together soon. Cool." Either getting back to one's life means everything caves back in on you so that you don't follow up with stuff you said you were going to do or you sit there and go "well, they're probably busy so I won't bother them." And all that positive feeling you had when you were actually with the person gets kind of trashed. Either that or the comment wasn't actually sincere in the first place - which is a hundred times worse.
These are exactly the kind of machinations that make me want to be a recluse. I think people should say what they say and mean what they mean. This includes me, because I can well imagine I've done the same things to other people and should just get a mirror before I start whacking at folks. But the fact remains; the stumbling way we communicate with each other - insincerity, insecurity, people who talk and never listen, or folks who are all "oh we just like everything you do," or "I'm looking at you but I don't know what the hell you're talking about and don't care enough to delve into your brain to find out" - is the biggest reason I have a tendency to walk away, go inside, shutter up, and let you have at yourself.
So it takes a while to get me in, and then alienates me when - once I'm in - we're going to stop altogether.
Makes me want to shut the door and turn on an old movie and to hell with you. Sucker me in and then disappear like that. Hmph. How dare you.
Humans bug the snot out of me. Makes me glad I'm glad I'm inhuman...
EDIT TO ADD; And on the subject of hosting and being in my home and whatnot... people need to realize that if I don't care, then you don't get an invite or you don't have the nod that there's an open door, come anytime. If you're here, you're in. And if you're in that means you are welcome and welcomed here. So don't get all stifled. You don't come into my house unless I want you here. So if you're here... you're in. Did that make any sense?
* - Unless you are in my home, at which point I transform into the perfect host, making sure everyone feels welcome - another skill that has been lost in the 21st century; being a good host to ALL your guests.