Happy birthday, indeed. In this sneak peek of Season 1, Episode 4 of Vanderpump Rules, Stassi and her closest friends head to Las Vegas for her birthday weekend, leaving Lisa short-staffed at SUR. The crew is having a great time until Jax crashes the party, dragging his drama with Stassi to the forefront. Will he be responsible for ruining her big bash in Vegas? Watch the preview to see what happens!