Which, really, tells you everything you need to know about that show: a little corny, a whole lot catchy, and, deep down, something you probably enjoy despite yourself.

I was a teenager in the late 1990s, a very peculiar time in pop music. Third-wave ska bubbled to the surface, and so did its second cousin, pop-punk. Metal rap was inexplicably popular, and Marilyn Manson had just hit. Believe me, there are elements of those years that we all wish we could forget. Reel Big Fish fell a little bit higher than that for me: catchy and fun, but particularly representative of a period in pop culture whose star I long assumed had faded.

There were bands that did ska harder (Op Ivy), and bands that did ska better (the Bosstones), but nothing marked the moment when the genre crossed over into the mainstream quite so perfectly as the days in 1997 that Reel Big Fish’s “Sell Out” played in near constant rotation on MTV. And nothing quite marked its death quite so perfectly as July 14, 1998: the release date for the soundtrack for “BASEketball,” which featured Reel Big Fish covering A-Ha’s “Take On Me.” (Speaking of late-90s stereotypes, take a gander at that soundtrack listing: Deep Blue Something? Smash Mouth? NERF HERDER?!)

To me, Reel Big Fish represent that self-aware place we all probably visited from time to time in high school: you want to fit in but you want to rebel, and here comes this band singing catchy tunes with a great big wink toward that angst you’ve worked so very hard to calculate. “It’s not so bad bein’ trendy, everyone who looks like me is my friend,” they sang on (what else?) “Trendy.” “Please don’t hate me because I’m trendy.” Like many an angst-filled 16-year-old in 1997, I both hated and loved Reel Big Fish for that very reason.

And here, ladies and gentlemen, is where this nostalgic rumination takes a strange turn: that 16-year-old Reel Big Fish fan is apparently not an extinct creature. I got older. Reel Big Fish got older. The audience at one of their shows, however, has stayed exactly the same age. The 9:30 Club on Monday night was a sell-out crowd full of teenagers screaming along to “Sell Out.”

This shocked me.

And I wasn’t alone.

Walking around before the show, I talked to teenagers and I talked to 30-somethings. For the former, the night was about watching any other popular band; at 16, they love the band for the same reasons I did back then. Rebecca Macleod drove 2 and a half hours to bring her 15-year-old daughter to the show from their home in West Virginia. “She’s really big about getting right up front,” Macleod said. “So we have to get here hours early.” For Macleod, who also performed the same service for her 20-year-old son, it was her fourth Reel Big Fish show.

And sure, the presence of the Aquabats as one of the openers had a lot to do with the crowd skewing younger — the lead singer of the Aquabats moonlights as the creator and director of Yo Gabba Gabba, so, uh, yeah, that’s all I know and let’s move right along now. Eight-year-old Cooper and 11-year-old Mack were sitting on the balcony before the show. Dad Chris, identified by Mack as the biggest fan in the family, had recycled his Aquabat Halloween costume for the night. “I thought there would be more people in costume,” he said, looking out over the floor from behind his blue Spandex top and mask.

But amid all the kids (and their parents), there were people like me: old enough to remember 1997 and maybe feeling a little nostalgic. Lloyd, 30, and Terrell, 30, remembered the late-90s fondly, “back when music was great,” Terrell said.

“We grew up listening to them,” Lloyd said. “That’s all we did was ride around and listen to them, and I never got to see them.”

Bill Shondelmyer, 27 and wearing a Mighty Mighty Bosstones T-Shirt, was there making up for lost shows. “Ska to me has always just been about having a good time,” he said. “I was too young for punk rock, so I got ska. I wish I could have gone to shows back then and appreciated it like I do now that it is past its prime.”

The thing is, it doesn’t matter how old you are: ska apparently finds itself a new audience every couple of years because it’s damn fun to listen to, to dance to, to sweat to. Up on stage on Monday, Reel Big Fish presided over a great big party, with members of the Aquabats and the other openers, Suburban Legends and Koo Koo Kanga Roo, wandering back on stage throughout the set to join in. They covered both “Brown-Eyed Girl” AND “Enter Sandman,” just because, hey, why not, half the point of ska is proving the point that you can skank to anything. They were the ringleaders of a three-ring circus that knows no fads, only fun and musical family.