If you have a birth mark on your butt that is fairly big does mean boys want to do with you?

The presence or absence of a birthmark on your butt does not determine whether boys want to have sex with you. Sexual attraction is a complex and subjective matter influenced by various individual preferences and factors, not just physical appearance. It's important to remember that nobody has the right to make assumptions or judgments about someone's worth or desirability based on their physical appearance.