How do I stop caring about what people say?

People often talk about me like very often i could just be walking to lunch at school and i would hear people talk about my forehead. they talk about a lot of things but this bothers me so much and then i think about it constantly and sometimes cry about it when im alone. I notice that my friends dont care when people talk about them and i am wondering how i can be like them and stop caring.
How do I stop caring about what people say?
Post Opinion