Jon didn't want to be a slut, so the entire week that Karyn was a dog, Jon tried her best to stay away from guys, who she was incredibly attracted to. The guys, as it turned out, were also very attracted to her too. It made it even more difficult to stay away from them.
When the week was up, Karyn changed back into herself, except that now she was a slut. And a week after that, Jon ended up having sex with a guy, so then she became a slut too.