In the season four finale of “It’s Always Sunny in Philadelphia,” the character Charlie (played by Charlie Day) writes and forces his friends to perform an absurd rock opera, “The Nightman Cometh,” in order to woo his longtime obsession, the coffee shop waitress.

The show’s fifth season premiered on Sept. 17, and on that night, the cast paraded around a minimally set stage at Tower Theatre in Upper Darby to perform a live rendition of the opera.

Charlie Day, Danny DeVito, Glenn Howerton, Rob McElhenney and Kaitlin Olson could not have appeared more comfortable in a bright yellow suit, a troll costume, a baby-blue onesie, cat eyes and an adult-size princess costume, respectively.

The sold-out crowd was in rare form, as audience members gathered around the bar, dubbed “Paddy’s Pub” for the night, before the show, not shocking behavior from diehard fans of a sitcom whose main action takes place in a dive bar and routinely involves excessive alcohol consumption.

The atmosphere of loud, drunk Philadelphians was fitting for a show that centers around characters who may arguably be the most offensive people on basic cable.

Guys in the back screamed obscenities at the opening act, Don McCloskey, twentysomethings bought alcohol for under-aged audience members and an obnoxious group waited in a sketchy alleyway until 2:30 a.m. for the cast to walk out to their tour bus.

As the crowd members poured into the theater, they were greeted by dancing Green Man, Charlie’s alter ego who sports a green Lycra body suit with absolutely no holes for necessities such as seeing or breathing.

The show opened with a sneak peek from the upcoming Christmas special, “A Very Sunny Christmas,” set for release on Blu-Ray and DVD on Nov. 17, and an exclusive screening of an upcoming episode from season five. The episode entitled “The Gang Reignites the Rivalry” featured the Flipadelphia flip-cup tournament and had thousands of strangers laughing in unison, intensifying the outrageousness of the already outlandish episode.

The musical began exactly like the episode and followed the plot loyally with the exception of a few additional musical numbers, increased profanity and bits of extra dialogue and backstage bickering.

While in the television version of the episode Dennis explains, “I’m eating because I’m uncomfortable,” the live performance offered a more detailed account of Dennis’ stress-eating. Audience members watched Mac rat Dennis out for consuming an exorbitant number of “baby Snickers,” much to the dismay of Charlie, the director, who warned Dennis that Lead Boy is supposed to be lean.

The scene of “becoming” between Dennis as Lead Boy and Mac as the Nightman was more shocking and explicit than the toned-down TV version.

The combination of the Christmas preview, the screening of the upcoming episode and the stellar live performance was enough to make the evening worth every penny of the upwards of $300 that some fans spent buying tickets on StubHub.

What truly added to the “Sunny” experience was the rambunctious audience who laughed together in anticipation of many shared favorites, such as Mac’s Nightman crossing the stage to showcase his karate skills.

Enthusiastic audience members arrived in dusters, baby blue onesies and one group even wore red berets and suspenders, resembling the outfits Mac and Dee wear as vigilantes in the season three episode “Bums: Making A Mess All Over The City.”

And the fun continued after the show in the alleyway beside the theater, where excited fans waited in hopes of meeting, greeting or at least catching a glimpse of the cast. One member of the crowd admitted that he was there to “network,” as he attempted to write the name of his comic Web series on the hands of random people around him.

The crowd thinned out a little over the two-hour waiting period, leaving only the most loyal fans in the dark alleyway. However, no one was prepared to witness a huge, drunk woman bolt through the metal barricades and flash the bouncers and entire crowd, shouting, “Kiss me, I’m deaf.” In unison once again, and in line with the moral depravity of “Sunny,” crowd members yelled “Get that out of here.”

The bouncers, in T-shirts labeled “Charlie work” to signify the manual labor that is relegated to Charlie, escorted the woman away, but within moments she reappeared in the crowd. Virtually everyone shifted to avoid contact with the woman, many losing their places at the front of the group just as the cast finally appeared.

She leaned over the barricade in an attempt to either kiss or bite McElhenney, sending the gang running onto the bus and denying the crowd its chance to glimpse celebrity. Security moved everyone to a further barricade to better safeguard the area, and once secured, McElhenney came out to thank everyone and tell them to go home already.

It is easy to imagine the gang drinking riot punch and wine out of a can on their tour bus while bagging on Sweet Dee, but in all likelihood, they were trying to get some sleep en route to the six-city tour’s fourth stop, Seattle, Wa. Philadelphia was the show’s third stop after opening in Boston on Sept. 15.