How do I stop people from thinking I'm a school shooter?

About a month ago, someone posted on Snapchat that they were gonna shoot up my school and everyone thinks it was me even though I don't even use Snapchat. My friends tell me I look like a School shooter almodt every day, kids I don't even know ask me if I would spare them when I shoot the school up, people act scared of me even when I don't know them, when ever I am interested in girls people always tell them I'm crazy and will shoot up the school and then they automatically don't like me. This has been a problem for 2 years now and I don't know how to stop it. I do have lots of depression at the moment. I was abused a lot my whole life, I was bullied through all of elementary school, I don't talk to people, I'm a loner, I wear all black, I listen to music like Korn, Slayer and Metallica. I feel like I am a nice person but people get the wrong idea because of the way I look. People say it's because I have ling hair. I grow my hair because I like to headbang and have my hair fly and stuff and I was also never a short hair fan. I don't understand why people would think I would shoot up a school when I donate to the ASPCA every month, I don't own ANY weapons, I don't even know how to work a damn gun... How do I change people's thoughts about me because it makes me feel so bad. I would never shoot up a School. Also I try to explain to people I would never shoot up a School and they always say something like "you look like a person that would walk into a School with a gun." Wtf...