Should adults have the right to read what you post on facebook?

Do you think or should adults like parents, teachers, college admissions have the rigth to read what you post on facebook/blog/twitter postings, websities or is it invasion of privacy? Well, I chose that it's invasion of privacy, but i quite dont know how to describe it, so I want to get peoples opinions on it and if you could please explain, also you also discuss the 1st amendment!! thank you!!