In a 1977 study published in The Journal of Personality and Social Psychology, researchers gave men a photograph of a woman before a telephone conversation. Some of these photos showed attractive women, others a less attractive woman. When the men had the phone conversations with the women, the men who thought they were talking to an attractive woman spoke differently, and the woman subsequently adapted behaviors stereotypically associated with attractive people. Basically, when the men thought they were talking to someone attractive, they changed speech patterns and conversation type, and the woman did as well. The women who were thought to be physically attractive came to behave in a friendly, likeable, and sociable manner in comparison with the women who were thought to be unattractive.
In short, how you think other people perceive you (or how they actually do, for that matter), changes how you act as well. Expectations of others play a role in how we behave. We don't consciously realize it, but we all tend to conform to the perceived expectations around us. People who are called the "quiet one" or the "adventurer" or the "life of the party," even if that's not what they are, subconsciously conform to those stereotypes. It's obvious how this could apply to race, gender, religion, and plenty of other characteristics.
All this is from the same Lifehacker article I've been quoting over the past couple of days. You could just go over there and read the entire article for yourself - after all. you're the inquisitive type - but you'd miss all my pretty pictures of Spanish boats.