With music created for — and especially by — teenagers, there’s a camouflaged vitality that makes the best stuff go fizz. It’s the common nucleus of hip-hop, punk and metal. It’s joy disguised as anger. It’s a laugh that sounds like a snarl. It’s ecstatic toughness.

This summer, you can hear it most clearly on hip-hop radio where Mississippi duo Rae Sremmurd’s “No Flex Zone” has been bursting from car speakers like so much New Year’s confetti. Over a twinkle-n-boom beat, the teenage rappers unload heaps of trash talk on anyone foolish enough to peacock in their immediate vicinity. “They knowww better!” goes the hook, which sounds like a territorial threat, but feels like an invitation to the party.

Teenage Mississippi rap duo Rae Sremmurd, Slim Jimmy, left, and Swae Lee, right. (Max Hilva)

This specific strain of kid-energy has surged through generations of rap music, but ecstatic toughness speaks to an almost universal teenage mode of being. Adolescence is a time when enthusiasm and defiance help us cope with an overwhelming sense of vulnerability — which is why kids get wild haircuts, pierce their faces, wear their pants funny, stake out turf in the food court, and play songs like “No Flex Zone” too loud on their earbuds. It feels good.

Youth may be the thing that adult fans of teen-centric pop fetishize most, but ecstatic toughness is what we actually value. You’re familiar with its powers if you’ve ever head-banged to Slayer’s “South of Heaven,” slam-danced to Black Flag’s “Rise Above,” or done both to Crime Mob’s “Knuck If You Buck.” These songs remind us of when our lives felt too small and our hearts felt too big. And because young people always feel that way, ecstatic toughness never goes out of style.

But this summer, “No Flex Zone” stands out because it tweaks the balance; it’s far more ecstatic than tough. The reverse is more common, as in the case of “Hot N—-,” the breakout single from 20-year-old Brooklyn rapper, Bobby Shmurda. His name alone suggests innocence, goofiness and menace, and his lyrics are grimier than any of the rhymes in “No Flex Zone.” But there’s still joyful magma gurgling beneath the pavement.

If you can’t hear it, look for it in the song’s video. After about two minutes of sinister gun talk, Shmurda flings his New York Knicks cap into the void and starts shimmying in his sweatpants. After spending plenty of the video stone-faced, his entourage goes all smiles.

[Warning: This video contains explicit lyrics.]

When skeptics of hip-hop struggle to locate the exuberance in songs like “Hot N—-,” it likely has to do with the fact that violence and misogyny have become the genre’s lyrical building blocks. Detractors don’t hear the humanity in the music, just knots of harsh words. And that rift, that inability to recognize the fundamental personhood of young black men and the vulnerability of teenagers in general, is especially jarring to consider against the events currently unfolding in Ferguson.

Art takes on new meanings as it gets siphoned through real life, and even though it was filmed before Mike Brown’s killing, it’s uncanny how elements of the music video for “No Flex Zone” feel like a response to it.

In the clip, the duo — Swae Lee, 19, and Slim Jimmy, 18 — are cruising down a leafy suburban street, surrounded by a protective CGI force field, an imaginary, sci-fi manifestation of their no flex zone. In a hip-hop culture that celebrates the intersection of fantasy and luxury, here are two black teens who have acquired the culmination of both: safety.

[Warning: This video contains explicit lyrics.]

More symbolism sprang up during a Rae Sremmurd concert I attended just outside Atlanta last Saturday night. As a tear gas fog was settling over Ferguson, roughly 570 miles away, Slim Jimmy came bouncing out onto the stage during the duo’s opening set wearing a gas mask. (Bobby Shmurda performed later in the night — he was wearing a delighted grin.)

The following afternoon, Rae Sremmurd and their producer, Mike Will Made-It, came gliding through the front door of a nearby recording studio, eager to work on some new songs. (For their moniker, the duo took the name of Will’s record label, EarDrummers, and spelled it backwards.) Before the recording session got underway, I asked Jimmy why he wore that gas mask on stage. “If I take it off in public,” he said, “all the girls come running at me.”

So standing out helps him stay anonymous? Or maybe he was cloaking a heavy political statement in a joke. Either way, this was ecstatic toughness as a fashion accessory. And what about the music? Was “No Flex Zone” written in a burst of elation, defiance, petulance, mischief, exhilaration?

Lee — a kid from Tupelo enjoying the ride of his life during one of the ugliest American summers in decades — bent his mouth into a cool half-smile. “We were just having fun with the music,” he said. “Like we always do.”

Rae Sremmurd performs at the Trillectro music festival at the RFK Stadium Festival Grounds on Saturday.