While this picture from Shoebox Blog is quite funny, it's really not much of an exaggeration of what's going on in real life. Facebook's (lack of) privacy settings have gotten worse over the years. Essentially, we have to treat everything we do on the internet as completely public. Times have changed and we have to change with them. If we don't, things we posted months or years ago on Facebook will come back to haunt us.
*Tip of the Day*
Google your full name in quotations every once-in-a-while, i.e., "[first name] [last name]" to see what's out there about you. Future employers and grad schools regularly Google the names of their applicants. Figure out what sort of information people can find about you and if any of it is problematic, try to remove it before applying anywhere for jobs or higher education.