It's 2016. While in certain aspects our society has become more diverse and open, we still continue to take steps backwards by binding people to their century-old stereotypes. It has gotten to the point that while there may be more gay people in your community, movies and television shows continue to only identify gay characters using stereotypical behavior.
Ultimately, stereotypes go beyond just trying to identify someone with a certain group and are only harmful to the person being stereotyped. We often are too consumed with ourselves to the point that we forget how some of our judgments impact other people. Being serious while saying comments such as "Oh, well she's wearing a short skirt, so she must be promiscuous," "He cares about the way he looks, so he can't be straight," or "She goes to church, so she must be an un-accepting conservative," is encouraging a behavior that isn't beneficial to society in any aspect.
Your identity is not determined by how you act or what you wear. It's okay if your interests align with your identity's stereotypes, and it's also okay if they don't. A guy can have feminine mannerisms or be into things that are thought of as "girly" and can still be straight and confident in their gender identity, just like a girl who may have more masculine mannerisms. Along those same lines, someone can have "gender normative" behavior and not be straight. It isn't fair to make assumptions about someone's sexual orientation based off of things that are on the surface--after all, you know what they say happens when you assume things.
My "blackness" has been put into question for as long as I can remember, due to my lack of experience and stereotypical behavior. I don't have black best friends, I belt One Direction songs everywhere I go and I speak clearly and grammatically correct. Because of this, I have often felt out of place. In middle school, I had similar interests as my white peers, but not the skin to match; I was often called an "Oreo" (black on the outside, white on the inside) or "the whitest black person" that person had ever known. I used to embrace those things, as I felt like I was finally fitting in, but I eventually realized that, regardless of what I liked or who I hung out with, I will ALWAYS be black.
I am not trying to act easily offended, and I understand that, for some people, stereotypes are all that they have known; they may have only seen a black person on TV, and have gathered an idea of what being black is all about by watching that program. Also, sometimes people mean well by the stereotypes they implement, like when your uncle asks you if you have a significant other of the opposite sex, and are not directly targeting you as a person. It's just important to be understanding to those that are innocent, as it is to try to avoid stereotypes as a whole.
If someone doesn't fit a stereotype, they may go through a lot in order to try to fit in, or it may cause them to feel isolated from the group of people to which they belong and cause them to question their identity/individuality. In high school especially, everyone is exploring themselves and figuring out where they belong, and stereotypes, whether you notice it or not, play a huge role in that process. While some people may be bulletproof when it comes to judgement from others, some people aren't as much.