Did you ever pet someone else's dog or cat? A dog goes 'I don't know who that is but, wow! Someone else to pet me!' A cat will be cold and standoffish, because that's how cats are. We had a cat who used to run to the door when he heard the doorbell, to see who it was. Then whoever it was he'd rub against their ankles or even jump onto their lap. Everyone said 'That cat must have been a dog in a previous life!'
Some people are just uncomfortable around people they don't know well. They might even be very polite (outwardly) but you can sense their discomfort. You can't do anything about that except hang around long enough for them to get used to you.
I always thought some people didn't like me at first because I have a weird sense of humor. When I'm laughing, I'm usually serious. When I seem serious, I'm often joking. If you don't know me, you wouldn't know! For me it's humor, for others it's other things.
Young people (teens) are often said to be much too susceptible to peer pressure. This is because, at this age, you don't have a good sense of yourself--your good and bad points, what makes you attractive or fun to be with or good to work with, so you pay way too much attention to what others think and say (by 'you' I don't mean -you- i particular). By your mid 20s you have more of an idea of what you're like, so you listen to others but make your own decisions.
It took me a while to trust myself. At work, some people liked me and would do favors for me, cooperate on some plan, etc., while others raised their noses in the air and treated me like a waste of time. Eventually I came to not feel responsible for how people treated me. I do the best I can, the rest is up to THEM. I found it easier to get along with people if I didn't care! Not to say I could treat them just any way I wanted. I was responsible for MY end of the conversation or relationship, not theirs.