Seopinghareo Gallae?

How did the phrase "Surf with me" became a connotation for "Sleep with me"? There are strange rumors​ surrounding Ha Doyoon, and Sung Jin, curious to find the truth behind those rumors, approached him. The events that unfolded during the 3 days that followed only made him more and more confused. (Source: Bomtoon, translated) Note: Part of Kidari Entertainment's "Yeoreumdanpyeonseon: Some in Summer (~키다리이엔티 여름단편선~ 썸인썸머, Kidari Entertainment Summer Short Story Collection: Some in Summer)"