Is there a psychological model or theory that describes strangers in the vicinity unknowingly causing discomfort? The closest thing I found to this is social anxiety or agoraphobia, which is a fear of socializing or a fear of public places, respectively.  However, I think the idea that strangers can cause discomfort by default is more a symptom of avoidance personality disorder.  What is the difference between agoraphobia and avoidance personality I wonder.

Agoraphobia seems more like avoidance personality disorder than social anxiety disorder, and yet more often agoraphobia is confused with social anxiety disorder than vice versa.  At least, if you go to Wikipedia, more information is found about social anxiety disorder than avoidance personality disorder.

My curiosity stems from the fact that a huge part of having avoidance personality disorder must involve seeking treatment, yet I read in a lot of places that people who suffer from it fail to seek treatment.  Since treatment of avoidance personality disorder seems to be so ubiquitous, it would be very easy for somebody with the disease to find somebody to help.  So what's the reason that it's not diagnosed more and if perhaps it is diagnosed more often and I just don't know about it, what explains why there is no widely understood treatment?
I think the answer to that question can be teased out if one knows the reason why the presence of or noticing strangers in the vicinity leads to feelings of discomfort.

What do you mean by "in the vicinity"?

Social psychologists have studied what is called proxemics. If we simplify it, one can say that they study the concept of "personal space". Mostly focused on two people interacting with each other, but there is also research on what is called cognitive spatial mapping.

I can think of multiple "diagnoses" that can be tossed around and played with. Schizoid personality disorder. Schizotypal personality disorder. A mild form or some pervasive developmental disorder (Asperger syndrome, for example). If the discomfort is not rooted in a fear of embarrassment or feelings of social ineptitude, it is harder to proximate the root of the discomfort, harder to put a label on it.

On a tangential note, going back to the topic of proxemics, people tend to have social conventions on what the appropriate distances away from others are; given the environment, closeness of the relationship, distance between or amongst people and yourself, etc. It is interesting to note that the same phenomenon (uh, exaggerated word) occurs in social interaction in a virtual world sort of setting. A well-known example is the study of proxemics in Social Life. When someone does not follow convention or simply violates another's personal space, even in Social Life, it generates discomfort. But I digress. Sorry, tangential ramble.