The Brady Bunch was a television show about a very normal and happy family. Britney refers to Britney Spears, a very troubled and out-of-control person (at least she was). Going from Brady to Britney means going from normal and controlled to being totally out of control

Lacy went from brady to britney today at work. I went from brady to britney and back before. The main character in the story goes from brady to britney. Some examples.