It means why have you done something.

why do you read this

When you mind your own business and do what brings you happiness and joy without worrying what other people have to say.

polite way of saying "go fuck yourself"

Doing something you want and beliveing that you can! Making your own path. You do you girl

A speech expression used commonly when someone is unable to remember the thing that they were supposed to do,
or when someone else forgot and you are using the phrase sarcastically.