I'm not going to answer the door when my parents visit
You don't want your parents to visit you at your house?
I want to be alone.
It is bad manners to not answer the door for your parents. This will cause them to worry about you. They are just there to stay for a few days and catch up on things.
I am grown, I don't need them anymore.
We all need our parents once in a while in our adulthood life. I'm a grown up but having parents when you need help makes our lives easier.