The first thing Jon could think of too try the unwishing stone out on was, of course, Karyn.
Jon thought about how Karyn had accidently enlarged her breasts to DD's. She'd kinda gotten used to them, but Jon had already thought about it. Only the wish didn't just reverse the wish, it took it further.
Karyn, laying back on her bed, suddenly felt a little loose up top as she watched her glorious mounds shrink from DD's to an A Cup.
Jon realized, he was not going to be welcome over at Karyn's for a while...