It starts with medical exams, Hydra doctors not-so-clinically stretching his ass and working his prostate, handling his cock and balls. They exclaim in disgust when he gets hard, calling it evidence of his degeneracy, and maybe they punish his dick/balls/hole or otherwise hurt him until his erection wilts. It's the same when they rape him: if he ever comes from the stimulation, he's taunted and maybe punished to correct his whorish tendencies. Eventually he prefers it when his handlers are brutal, because it's easier without the chance of pleasure—the shame he feels is less sickening. Worst, of course, are the handlers who deliberately tease and excite him, driving him over the forbidden edge no matter how hard he tries to hold back and then calling him filthy when he comes.

Bonus: one imagines this sort of treatment might leave a lasting impression.