Need to give Jon a sexual fixation on the idea of watching other people pee.
There’s something about how humiliating it’s considered to pee in front of another person, especially on accident, that simultaneously compels and repulses him. And sure, sometimes he gets a little wet (ha) when he thinks about publicly pissing himself, but mostly his thoughts go in the reverse. What would it be like to see someone’s pants become stained with urine as they wet themselves? What would it be like to spy on someone in a bathroom stall, or watch as they use a urinal? To see something private and gross and humiliating? I think he has regular fantasies where he discovers some secret hole in the wall where he can watch as person after person walks over and pees directly in front of him while he masturbates, and a key component of the fantasy is that they don’t know he’s there and would be upset and horrified if they knew that he was spying on them or what he was doing while he watched. And he feels like such a guilty miserable creep for it too.