They are afraid to be judged wrongly
People might feel uncomfortable around strangers because they are too afraid to be judged by them. The more a person cares about his public image the more likely will he feel uncomfortable around strangers.
They aren’t sure how will others react to their falws
All people know they have certain flaws and some of them worry too much about them. A person who isn’t sure how will others react to his flaws he might feel uncomfortable around them until he gets an answer to his worries.
They are introverts
Introverts can find it more difficult to get a long with people they just met. They usually take their time before they feel comfortable around others.
Shyness & low self esteem
Shyness & low self esteem can make a person feel uncomfortable around others. Shyness and low self esteem usually go hand in hand and make some people very uncomfortable around the ones they just met.
They remind them of people who weren’t very friendly to them
Sometimes a person unconsciously gets reminded of a past relationship as soon as he sees a stranger. If the unconscious memories that flashed in that person’s mind weren’t unpleasant then he will not feel comfortable around that new person he just met.
They want to be accepted
People who want to be accepted in a certain group or who want more approval than others will usually feel very uncomfortable around strangers because they care a lot about fitting in.
Poor social skills
A person who has poor social skills, who doesn’t know what to say or who can’t handle social situations well is very likely to feel uncomfortable around strangers. The feelings come from the fact that the person is too afraid to mess up.
The strangers are significant to them
If a person met random strangers whom he doesn’t care about then most probably he won’t feel uncomfortable. The more important the random strangers are to the person the more likely will he feel uncomfortable around them.
They feel inferior to them
People who feel inferior to others can have problems feelings comfortable around them. The more the perceived different in worth is the more unpleasant feelings will the person experience. (See What Causes an Inferiority Complex?)
They are afraid to be themselves
People usually feel at ease around their friends because they can be themselves. Some people feel uncomfortable around strangers because they aren’t sure whether being themselves would be a good idea or not.
They think they might be mean to them
If a person expected a stranger to bully him, be sarcastic or mean to him then he might feel uncomfortable around that stranger. Poor past experiences with others can result in that way of thinking.
They are afraid to act or look clumsy
So many people feel anxious around others because they are too afraid to look or sound clumsy. Being very self conscious of one’s actions during encounters with strangers can increase the feelings of discomfort. (See What are the body language signs of fear?)
They believe everyone is watching them
Some people mistakenly believe that all people are watching them and focusing on their moves. This kind of thinking results in excess self consciousness and as a result a person might feel very uncomfortable around strangers.
10 myths about psychology, debunked by Ben Ambridge | TEDxYouth@Manchester