by SpecialtyM3
With all respect for creative liberties, if a story is fundamentally implausible, this distracts me from enjoying it. A speedo suit is basically a figure 8 around both legs. Strain is primarily on the short side seams on each hip. For it to become a slingshot, the crotch seam would have to be open already (turning the figure 8 into a ring around the waist) when one side seam rips: in that case, it may well shoot in the direction of the hip with the remaining seam, otherwise it will remain around the other leg, or if both side seams rip, it will simply fall down. But that would mean it had already turned into a loincloth before, or because the elastic fabric contracts, it will become more like a belt, already exposing his dick. This was not written but it can't possibly go unnoticed by him and others. Also, the softer and stretchier the fabric is, the less force is generated; for it to become a slingshot with any relevant force, it would have to be a tough elastic, digging deeply into the waist, but the story says it is very comfortable.
I initially expected that the white front part would become transparent after dipping into the water, exposing him that way.