A celebrity free pass is an agreement between you and your significant other that if you meet said celebrity and there is an opportunity to sleep with them, your partner cannot get mad at you for doing so because you had agreed before hand that this person was your celebrity free pass. It is ideal if both of you in the relationship choose a celebrity free pass so that the playing field is even.
Julia met Drake at a bar, and hooked up with him, knowing that her significant other could not be mad at her, because Drake was her celebrity free pass.