I am guilty of doing this and it is believed that in the first 7 seconds of meeting you they have a solid impression of you.

I am terrible for judging people from their first impression and it takes me a long time to change my opinion. Most of the time my initial judgement is correct but I do think I probably miss out on making new friends because I am too wary of the harm people can do to your life if you let them in.

Am I just a snob? Should you ever judge a book by its cover?