Okay, people get really confused with the term "caring what people think" these days. You have to care what people think. If you didn't people would be running around the street butt-naked posting porn flyers everywhere and giving their phone number to random strangers to come watch them have sex with their daughter. There are so many things wrong with that, and the exact reason why it doesn't happen is because there are norms in society, laws you have to follow.
Now, when it comes to things like "omg if I wear this shirt will people make fun of me?! ;_____;" that's dumb. I don't really care what people think of me and I do what I like to do, but I obviously follow norms and society's rules.