Barely Legal is episode 08 of family guy season 05. It was originally aired on December 17, 2006.
When Meg can’t find a date to her junior prom, Brian gets suckered into going with her, even though he is dating Jillian. When Brian arrives at the dance he gets drunk to ease his pain, but after he makes out with Meg he really hurts. The next morning Meg starts to think of Brian as her boyfriend and becomes obsessed with spending every waking moment with him. Meanwhile, Peter, Cleveland and Quagmire join the police force and have to come to Brian’s aid.