There is no magic answer here. Unfortunately people tend to make quick judgments based on first impressions. This often includes an assessment of appearance.
Although it is unfortunate that people can be mean and prejudiced sometimes, I tend to think about it this way:
I am happy with myself and confident enough about myself to not take it to heart every time someone ignores me or doesn't give me the respect I know I deserve. This does not work every time and we learn to develop thick skins. It is also ok to let it overwhelm ourselves occasionally and seek comfort and love from our close friends and family, that's why we're here after-all.