Scout Willis prefers to go swimming in her birthday suit. On Monday, August 26, the singer was nearly naked when she filmed a video of herself for an Instagram Story that she cheekily captioned, “Loves a tan line, hates a bathing suit.” The brunette beauty, 33, was wearing nothing but a low-rise maroon sarong in the video and had her long locks strategically covering her chest. It was just 10 days earlier that Willis was donning a bikini in a social media video that acted as a birthday tribute to her older sister, Rumer Willis, 36. “Best mama, hottest mama, best friend, bravest, funniest, smar…