When you think of the occasion for long sleeves, a few things come to mind: church, a job interview, or the first time meeting your S.O.'s parents. One thing that may not come to mind: the beach. And yet, there seems to be something in the water (zing!) because we keep noticing our favorite celebs sporting a certain type of long-sleeved swimsuit, and have spotted plenty of trend-forward takes on traditional rash guards when we search "swimwear" at the coolest boutiques. We wanna know: what's the deal?