An internet meme, similar to "I'm 12 years old and what is this".
It originally started on the website mylifeisaverage.com when a poster said that their 9 year old daughter read the website and that the other users of the site should watch what they said.
It is used as a joke when something inappropriate or something using cuss words is posted.
Person 1:Omg, I'm so badass.
Person 2: My 9 year old daughter reads this!