The stone worked just as it was supposed to, so since Jon wished to be a very masculine guy and Karyn was the next one to touch it, she got the wish and it was interpreted by the stone as if she had wanted the wish.
Jon took a hold of the stone and felt a strange tingle, but did not pay much attention to it as he was concerned with Karyn's changes.
Before his eyes, Karyn when from being a very hot woman, to a very masculine male, and because the stone was acting on Karyn on the wish Jon made, and because Jon did not have any nonreversible wishes on him, the breasts and hair on Karyn changed.
Since Jon had worded the wish, "I wish I was an extremely masculine guy" the stone granted the look of Jon to Karyn as the base template, before adding more height and muscular strength. The rock embellished the wish a bit and filled Karyn's very masculine pants with a very large masculine appendage.
But, the rock was not done just changing Karyn.
Since Jon was the next to touch the stone after Karyn's wishes to be very feminine girl the kind that always wears makeup and only wears skirts and dresses and I always had the newest fashions and that she could join the cheerleaders, those wishes were going to Jon. And, again, since Karyn had worded it using the I, she was the base template for the new body Jon would receive, and the rock had to take into account the restrictions imposed by her long blonde hair and large boobs that she had from before, since she was locked into having them.
After all the changes, Jon looked like:
