Everyone has a filter in their head. Whatever they see or hear goes through a filtering process and whatever they say goes through a filtering process. For e.g. when speaking to a professor you wouldn't use foul language, your brain automatically filters your words that come out. While talking to your friends there would be a different filter on, so and so forth. So when our brain gets some information it gets filtered, thats why we are stereotypical of people. Its been fed in our brain that Arabs are rich, Blonde's are stupid, Indians are smart etc. But this is not true, all Arabs are not rich, all Blond girls aren't stupid, its an equal probability that a Brunette is as stupid or smart as a Blond. All Indians are not smart, all Indians don't own businesses.
This song shows some of the stereotypes that are in the world.
This picture represents some actions that make them a prey of stereotypes. When we see a person who has been stereotyped before it is already set in our brain that that person has that trait in them which could be totally untrue, but to remove these notions it is very difficult and therefore there are so many people who judge others just on their appearance or gender or race.
I am aware that whenever I walk around or into class, someone is judging me or putting me into a category where I might not even belong. This is life and we have to deal with it.