The D.E.N.N.I.S. System

"The D.E.N.N.I.S. System" is the tenth episode of the fifth season of the American television sitcom It's Always Sunny in Philadelphia. It is the 55th overall episode of the series, and was written by executive producer Glenn Howerton and series creator Rob McElhenney, and directed by series producer Randall Einhorn. It originally aired on FX on November 19, 2009. The episode features Howerton's real life wife, Jill Latiano, as the subject of the titular system.

The series follows "The Gang", a group of five misfit friends: twins Dennis and Deandra "(Sweet) Dee" Reynolds, their friends Charlie Kelly and Mac, and Frank Reynolds, Dennis' and Dee's legal father. The Gang runs the fictional Paddy's Pub, an unsuccessful Irish bar in South Philadelphia.

In the episode, Dennis reveals his foolproof seduction system to The Gang, the titular "D.E.N.N.I.S." system, with the example of Caylee. Charlie tries to use it on the Waitress but doesn't quite grasp the concept. The Gang tells Dee that her boyfriend, Ben, from "The Gang Wrestles for the Troops" is using the system on her, and Mac and Frank reveal their parts in the Dennis' system. The titular system is followed up in the fourth episode of the sixteenth season, "Frank vs. Russia"

Plot
Dennis (Dennis Howerton) walks in Mac (Rob McElhenney), Frank (Danny DeVito) and Dee (Kaitlin Olson) asking Charlie (Charlie Day) about the Waitress (Mary Elizabeth Ellis), whom he is in love with, and plays them a voicemail message of a woman, Caylee (Jill Latiano), who says she hopes he dies. Dennis claims Caylee is in love with her, but Dee argues otherwise, leading Dennis to explain his system for seduction to The Gang, called "The D.E.N.N.I.S. System."

Dennis explains that he met Caylee at the pharmacy when he pretended by buy pills for his sick grandma, which is the first step of the system. He convinces her into having pizza at his place, where they soon have sex. He then creates up a fake threatening neighbor to scare Caylee and makes her depend on him, only to soon neglect with her as she grows more attached. Dennis romantically show up to the Caylee's window and begs for forgiveness, and they later have sex again, before he sneaks out in the middle of the night with the intention to never talk to her again. He claims that the system leaves the girls loving him more than they would've before, but Dee, skeptical, challenges him to follow through with the system and get Caylee back. The Gang then convinces Dee that her boyfriend, Ben (Travis Schuldt), is using the system on her.

After Dennis fails to win back Caylee, Mac and Frank tell him that they have a system where they have sex with the girl after Dennis. Ben takes Dee out on a picnic, but she runs away after fearing that he's using the system on her, and spends the night in the bush. Charlie, misunderstanding the system, breaks into the Waitress' apartment and offers to fix her garbage disposal that he broke. Dennis then devises a plan to fix everyone's respective problems by going to the fair. At the fair, Dennis hires an elderly lady to pretend to be his grandma in attempt to win back Caylee, while Charlie fails to impress the Waitress and Frank dresses up as Dennis' pretend doctor. Dee gets stabbed by a carnival worker while flirting with him to make Ben jealous. In the end, Dennis' plans for him to win back Caylee, Charlie to win over the Waitress and Dee to make Ben jealous all fail.

Production
The episode was directed by producer Randall Einhorn, and was written by executive producer Glenn Howerton and series creator Rob McElhenney, all of whom are main actors in the series. The episode features Howerton's real life wife, Jill Latiano as Caylee, though they weren't married at the time of filming.

Reception
The episode was watched by 1.49 million viewers on its initial airing. It was received generally positively, with IGN saying "Always Sunny was out in full force", although contrastingly stating "a large chunk in the middle ... just felt flat". They rated the episode a "good" 7.8/10. The A.V. Club called it an "amusingly intricate plot", while also commenting on it being "little lighter on laughs than" the previous episodes, and giving it a B+. Entertainment Weekly and Rolling Stone rated the episode 6th and 18th on their respective lists of 20 Best It's Always Sunny in Philadelphia episodes.