Kardashian, 30, appeared to be wearing a red one piece bathing suit, throwing up a peace sign, while Disick, 31, had on an orange life vest, jokingly pointing at the camera.
"Lifeguard on duty! #SurfBoardSurfBoard #PrivatePartySwim #TheLord #TheLady," Khloe captioned the picture on Instagram.
Nowhere in sight was Khloe's sister and Disick's longtime, currently pregnant, girlfriend Kourtney Kardashian, but chances are the picture was all in good fun. The sisters are currently filming "Kourtney & Khloe Take the Hamptons," and Disick has always been close with Kourt's younger sis.
Khloe is currently dating rapper French Montana, who gifted her a new Jeep and $30,000-worth of jewels for her 30th birthday.
In the past year, the father of 4-year-old Mason and 2-year-old Penelope lost both of his parents, and Khloe went through a painful split from husband Lamar Odom, which has bonded the two on the most recent season of "Keeping Up With the Kardashians."