For around a decade, “It's Always Sunny in Philadelphia” has had a lurking presence in the background of American sitcoms. The show was recently renewed for a 13th and 14th season, which will make it tied for the longest-running American live-action comedy series. Granted, it's tied for this spot with the little remembered “The Adventures of Ozzie and Harriet,” but staying on air this long, especially in today’s significantly more competitive TV climate is a special achievement. The show debuted on air around the same time as the American version of 'The Office,' and similarly brought a laughtrack-free format to the table. Revolving around five main characters known as 'The Gang', each with their own deplorable sides to their personalities, the show has memorably been coined 'Seinfeld on crack.' The show truly lived up to this moniker with an episode where a couple characters get addicted to crack with the goal of qualifying for government welfare. 'It's Always Sunny' is certainly not your typical lighthearted comedy.

One aspect of the show that deserves mention is its enabling of the late-career resurgence of Danny DeVito. While a staple in numerous films in the last couple decades in the 20th century, people thought Devito's career was basically over ten years ago. DeVito then made his shocking entrance onto "It's Always Sunny' as Frank Reynolds, a brash former businessman who is constantly coming up slimy schemes to make some extra cash. Together with his totally depraved lifestyle choices, DeVito added a new layer of outrageousness to the show, never failing to shock viewers with his ridiculous antics. It's a hard performance to live up to when DeVito, now 71, is willing to tear his way out of a leather couch, naked and smothered head to toe with oil.

More generally, 'It's Always Sunny's' unique place in the sitcom world is due in large part to the way the show is run. It is directed and produced by two of the main actors, Glenn Howerton and Rob McElhenney. Combined with the fact that a substantial amount of the dialogue is improvised, there is feeling of organic spontaneity that characterizes the show. Actor Charlie Day has also contributed his natural musical talent toward 'It's Always Sunny' with 'The Nightman Cometh,' a hilarious musical with subtle implications that his character was abused as a child. With a cast that has full creative control over the show, 'It's Always Sunny' never fails to produce highly original content.

'It's Always Sunny's' unique brand of dark humor can even provide us with insight into why humans find certain things funny. Common sense would probably tell us that an event is funny when something happens contrary to our expectations in a clever way. This doesn't seem to explain the variety of humor featured in 'It's Always Sunny,' where jokes regularly revolve around 'The Gang's' morally depraved behavior that we should rightfully feel disgusted by. A satisfying explanation might be found in the 'Benign Violation' theory of humor, proposed by researchers from the University of Chicago. According to this theory, there are two elements that make something funny. We are first presented with a 'violation' of some sort, where our moral, social or linguistic expectations are betrayed. The second element that comes into play is when we are reassured that the situation is non-threatening, either because you realize it happened to someone else, or isn't actually occurring in reality. When these factors occur simultaneously, the result is humor.

The typical scenarios in 'It's Always Sunny' fit this model well. While the actions the characters violate our intuitions about social norms, at the same time we take comfort in the fact that we are not the ones committing the violation. The TV screen serves as a symbol that separates the events in the show from reality, further adding to our reassurance. Dark humor excels in highlighting a jarring contrast; the more extreme the violation, the funnier the event is upon the realization that it's non-threatening. Despite its relatively small cult following, 'It's Always Sunny' tests and pushes the boundaries of what we find funny, cementing its place as a classic sitcom.