Juu just getting back from a long walk, he's about to head to the bathroom when he gets distracted by Tora causing a ruckus in the bedroom. One thing leads to another, and they have The Sex(tm). Juuichi suddenly remembers he really has to go, but it's also kinda...awkward to say "sorry i need to piss" in the middle of sex, and his erection helped him hold it in, so he thought it'd work out.

Long story short, Torahiko is never gonna let him live down the time he "fucked the piss out of him" and "brought the pool indoors". Juu, on the other hand, feels the looming terror of realizing that it was kinda hot in the moment.