The characters of It's Always Sunny in Philadelphia are not good people. Part of the show's charm is that they are entertaining in their terribleness, but they almost always face some kind of consequence for their actions. The central group of the series, which is the longest-running comedy on television, is made up of five main characters. Together they own and operate an Irish pub in Philadelphia, but mostly they get into schemes in pursuit of their selfish ambition.
Dennis Reynolds, played by Glenn Howerton, is best known for two key things, his rage and the D.E.N.N.I.S. system for chasing women. 'The D.E.N.N.I.S. System' is the tenth episode in Season 5 of the series, and its primary focus is on Dennis' explanation and execution of this scheme. While the actual system is pretty horrifying, the episode is one of the series' best and most popular for encapsulating elements of the gang's dynamic and Dennis' unique and controversial approach to sex and relationships.
What does D.E.N.N.I.S. Stand For
Dennis reveals to the group that he uses a specific system to seduce women. It's a long-term plan with predetermined steps, which are easily explained using the acronym he named for himself, which he calls the D.E.N.N.I.S. system. Each letter of his name stands for a step in his plan. The D stands for "Demonstrate Value." At this step, he uses a ruse to let a woman know he could be useful to her. The E stands for "Engage Physically," which is when he enlists Mac's help to manipulate the situation so that the woman will go to his bedroom with him, where they will hook up.
"Nurture Dependence" is the first N, and it's a particularly manipulative tactic where he will use anonymous phone calls or the like to make the woman feel unsafe on her own, leading her to depend on Dennis for safety. The next N is the opposite, it stands for "Neglect Entirely." At this step, he continues his tactics from the previous step but fails to show up for her in her time of need with the hopes of emotionally distressing her. The I stands for "Inspire Hope," meaning to sleep with her again, he shows back up in her life and gives a speech about how the neglect came from a place of fear and that he does love her. Then after sleeping with her again, he moves onto the S, which stands for "Separate Entirely," where he moves on and chooses never to see her again.
How Do Mac and Frank Take Advantage of the D.E.N.N.I.S. System
In the same episode, Mac reveals that he has his own system, which serves as a sequel to the D.E.N.N.I.S. system. So while he doesn't execute the system at that time, he still uses it to his advantage for the M.A.C. system. M.A.C. stands for "Move in After Completion" because he waits for Dennis to complete his system, and then Mac seduces the girl Dennis has just "Separated Entirely." Mac meets these women during the "Engage Physically" step, where he lays the groundwork to be perceived as a caring and sensitive rebound opportunity for them.
Frank Reynolds also takes advantage of these now vulnerable women and seduces them after Dennis and Mac have moved on. It's a sleazy system all the way through that manipulates random women and involves them in a web of lies and predatory tactics. It's ironic that Dennis is so annoyed with how Mac and Frank have inserted themselves into his system, considering his actions created the situation in the first place. "The D.E.N.N.I.S. System" episode is an excellent snapshot of the series and how the characters feed off each other's bad behavior to escalate the depravity to new heights.