Operant conditioning is the force at work behind Iason's relative inability to tame Riki using punishment because, almost without fail, the two of them wind up having sex after Riki's punishment. It might seem to the casual observer that the positive punishment Iason is administering would be a negative consequence for Riki and thus decrease the chances of his bad behaviour reoccurring, however this is not the case.
("Positive" in this case does not mean "good" it means "addition", which translates to providing an unpleasant stimulus, such as spankings in order to punish; negative punishment then being the removal [subtraction] of something