'Always Sunny' Hilariously Revisits Classic Bit More Than 13 Years Later

"Always Sunny in Philadelphia" aired one of its best episodes in years Wednesday night.

The hit FXX comedy is currently in its 16th season, and episode four - titled "Frank vs. Russia" - featured two main storylines:

Frank attempts to beat a Russian chess master and Dee and Mac both attempt to pick up men.

After more than 13 years, "Always Sunny" returned to the well and gave fans the inverse of the D.E.N.N.I.S. System.

The 16th season of "It's Always Sunny" is currently airing. (CR: Patrick McElhenney/FX)

"Always Sunny" presents fans with the S.I.N.N.E.D. System.

Every single fan of the legendary comedy series knows D.E.N.N.I.S. System episode is an all-time classic. It's one of the show's greatest moments.

That's saying something considering there are almost too many epic moments to count. Dennis' tried and true system to manipulate women into having sex with him before cutting and running is a classic example of comedy refusing to apologize.

The system is exactly what you'd expect from a narcissist who lacks empathy. It was first presented in the 10th episode of season five. It's been referenced since and Dee did her own spin on it.

However, everything came full circle with Frank vs. Russia." Dennis, for reasons that aren't clear, also has a system to pick up men.

You know what Dennis is spelled backwards? It's sinned. It all makes perfect sense!

"It's Always Sunny in Philadelphia" introduces fans to the S.I.N.N.E.D. System. (CR: Patrick McElhenney/FX)

This is a genius callback for the show.

Without spoiling how it all plays out, it was honestly genius for the "Always Sunny" crew to return to the well with the S.I.N.N.E.D. System.

It did two things. Reminded viewers is as dark and twisted as ever, which is made clear in a storyline involving a sex toy and Mac, and it also was a huge nod to all the fans who are still with the FXX comedy after 16 seasons.

It truly felt like the episode was crafted as a throwback and thank you to everyone who has stuck around.

"Always Sunny" returns to its old ways with newest episode. (CR: Patrick McElhenney/FX)

"Always Sunny" is still great. Don't get me wrong, but it's not a secret it doesn't throw the same heat as the early season.

This episode felt like an episode from more than a decade when the show truly didn't care. After more than 13 years, the series returned to its roots with D.E.N.N.I.S. and S.I.N.N.E.D. systems.

Now, we need an entire episode dedicated to revisiting the implications of dating on open water! It was touched on during the cruise episode, but definitely time for a refresher.