Courtesy “Bayside! The Unmusical!” The students of Bayside, with Mr. B.

It’s not every musical that has even the house band cracking up, but last night at a packed Kraine Theater, “Bayside! The Unmusical!” did just that with its raunchy, irreverent send-up of “Saved by the Bell.”

The zippy one-hour production – back after an earlier run in May – starts by reintroducing the archetypes of the early-90s sit-com: Zack Morris (JD Scalzo) is the naïve “cool guy” in acid-wash jeans who thinks his ditzy cheerleader girlfriend, Kelly (Caitlin Claessens), is a virgin even though a giant, er, “zit” on her stomach keeps her from going to homecoming. Slater (Israel Viñas) is the “greasy, sexy stud-muffin” who just wants to be respected: “I want to go to collage someday,” he mispronounces. Lisa (Shamira Clark) is the bubbly token black girl who does nothing but shop and gossip while fending off Screech, the nerd who, appropriately enough, is played by lanky comedienne Rachel Witz. And Jessie, well, she’s another story entirely.

The stereotypes quickly come undone like a defective Trapper Keeper: for all its Disney Channel-esque cheeriness and its “uncomfortably Christian creator” (per “Bayside’s” program), “Saved by the Bell” is the show whose cast members went on to get naked in “Showgirls” (Elizabeth Berkley) as well as in an honest-to-goodness porno (Dustin Diamond). “Bayside” revels in that, via an almost Benny Hill-like parade of slapstick hormones and homoeroticism: the kids need to raise an “unreasonable” amount of money (a whole $500!) to save their favorite diner, The Max, and their ideas range from gay prostitution to stripping to pornography.

Courtesy “Bayside! The Unmusical!” Jessie feels the need for speed.

Nobody thinks to deal drugs, but caffeine addiction naturally takes center stage when Jessie starts popping pills. April Kidwell, who bears an uncanny resemblance to her “SBTB” counterpart, Elizabeth Berkley, steals the show as the manic, maniacal Jessie, channeling Kristen Wiig in her off-the-cuff kookiness. (It was during Jessie’s infamous butterfly metamorphosis that the band members, who happen to be the show’s writers and directors, Bob and Tobly McSmith, lost it a second time.)

Jessie isn’t the only character that goes off the rails: at one point the eternally copacetic Lisa discovers she’s black, decides Lisa Turtle is a “slave name,” and assumes the identity of “Oprah X,” eventually launching into a free-style rap that ends in an over-the-top call-and-response of “White!” “Devils!” (Yes, there’s a bit of “South Park” in all this.)

Courtesy “Bayside! The Unmusical!” Zack and Kelly.

Where identity politics are concerned, though, Slater is the running joke. He cites the “power bottom” as a wrestling move, is a little too eager to lock legs with Zack, and finally dons a rainbow leotard during Bayside’s talent contest. Meanwhile the girls reenact the famous aerobics-video episode: “You can pause and rewind this scene,” they sing flirtatiously, “just remember we’re only 17.”

“Bayside!” is full of those sorts of in-jokes and self-references, to the delight of “Saved by the Bell” fans. At one point the cast sings, “It’s a dream sequence; it has nothing to do with the plot! It’s a dream sequence; we have them a lot!” There are also outside references to the Fresh Prince, Alf, and, best of all, 4 Non Blondes, via a musical rendition of the perverted principal Belding’s catchphrase, “What is going on here?”

So what is going on with “Bayside”? A hell of a lot of ribald fun. Rest assured, you won’t need caffeine pills to get through it.

“Bayside! The Unmusical!”, Oct. 9, 10, 16, 17 at Kraine Theater, 85 East Fourth Street (near Second Avenue), $15