According to Jim Recap: The Jealous Husband
When Jim and Cheryl go out to eat with Ryan and Dana, Ryan gets a big dose of Jim's wisdom: He sees how Jim sometimes will act jealous in order to show Cheryl that he still cares. Unfortunately he misses the other part of the lesson and doesn't realize that he isn't supposed to do it until after he and Dana are married - and when Ryan tries the trick on the guy at the coffee shop, Dana thinks that Ryan is a psycho.
Naturally, there is only one thing to do, and that is to let Jim try and fix it. They slip the guy at the coffee shop $50 to pretend that he actually thought that Dana was hitting on him. That, in turn, makes Dana think that maybe Ryan was right, and that gets him back in her good graces long enough to get things going again. Unfortunately, Ryan tells her all about the details, despite Jim and Andy's warnings.
Luckily, Dana doesn't spill the beans to Cheryl, because she wants Cheryl to be happy, and as strange as it sounds, Cheryl is happy playing the little "game" with Jim. So things stay the same - but Jim isn't allowed to give Ryan anymore advice.
