When someone says something mean about you, how do you shrug it off?

Everytime im at school and im walking down the hallway i'll always hear some rude comments from other boys. things like ewww she ugly, and she looks like a dog. i try not to let it get to me but sometimes hearing those things are hurtful. i personally dont think that im ugly. i kno im not preety but i think that im okay , and i kno i must not be that ugly if ive had boyfriends in the past. so when i hear people say these things how can i just shrug it off and not let it get to me. im trying to make myself have a higher self esteem