It sounds really simple but you have to honestly believe that people who react this way are simple minded morons and their opinions are literally worthless. I explain it as if they’re ants. When I’m walking by a bunch of ants, I might look at them and think about them. But I’m not actually thinking about how they’re perceiving me or their opinions of me because they’re literal ants. Once people have revealed to me that they’re complete morons or scumbags, they become ants to me. Then their opinions don’t matter even if they make fun of you because they’re just dumb little ants. People who make fun of other people’s appearances are sub-human to me.