Sometimes, when you meet someone that you never met before in your life, I bet you would have some bad impression to the person. Even I always do this when I met someone new. I tried to follow the "Don't Judge A Book By It's Cover" quote, but it doesn't work. Well, not never, but sometimes, I managed to follow it. It's an awful thing to do to someone that you never even met before. I often done this thing in my own way, which after I know the person, I will tell him/her about my first impression on him/her. It's a fun thing to do, but when you used the wrong words, maybe he/she will explode into anger.
My point is, don't judge people from their looks and the way they act. The inner-thing is the most important thing that you have to know. It's not about the look on their face, it's the inside of them.