I think that something about the idea of wetting himself would really do it for Jon. Desperately trying to keep himself composed even as his bladder gets more and more insistent. The loss of control. The humiliation. His weakness and embarrassment known to all and there’s nothing he can say or do to make it better, because he pissed himself in front of all his coworkers, in front of his boss. Sitting in a pool of his own urine and wallowing in shame. I think he’d fantasize about it, and he’d feel a combination of terror and arousal at the idea.