Things took off at around 1 p.m. with D.C.'s Modern Man and then U.S. Royalty. It was the second music confab organized by Sweetgreen, and much bigger than last year's, which took place at a tent in Dupont Circle in D.C.

Merriweather's slippery lawn was mobbed with a mostly young throng of people who had paid $55 for their tickets. Admission to the amphitheater, which was also mostly filled to capacity,  cost $100.

Because there was only one stage, there was a lot of waiting around for bands to set up.  The Strokes took the stage at almost 9 p.m., nearly 45 minutes after Gregg Gillis (Girl Talk) left the stage drenched in sweat.

In the meantime, crowds inside the amphitheater entertained themselves playing long-distance beer pong with neighboring aisles (at right). They seemed to want to keep going when the lights dimmed for Casablancas.

Gillis had finished his set as if it was the last one of the night. In a typical flourish, he dropped beach-ball-sized balloons on the audience, and for the second time, confetti. After Gillis' jittery show-boating, Casablancas was almost comically insouciant. His mic malfunctioning on first number "Is This It," he instead muttered "Is this on?" on the chorus.

He didn't even pretend a rapport with the audience. His first spoken words of the night came before the fifth song, and they were well-practiced platitudes. "You guys are the best we've played to," etc.

Still, the show was visually appealing and the band hit all their notes.  Like the festival they were headlining, they were diligent, and only occasionally memorable.  Arguably, they peaked here (as elsewhere) with "Hard to Explain," a song released when the high-schoolers in the audience hadn't even hit puberty yet. They didn't match, in energy or commitment, Lupe Fiasco's set mid-afternoon, right before Girl Talk.

Only here would a mash-up DJ with no commercially released material be scheduled after a rapper with three albums on the Billboard 200. Fiasco, who performed in cammo cargo pants and a jean jacket emblazoned with "Laser Club," delivered a scorching performance that left no audience member unturned.

The crowd seemed to be chanting along to every song, but was loudest on "Superstar." Fiasco said he'd written the song while he was depressed, urging the audience to seek help when they feel like that. "No grade is worth your life," he said to thousands of shrill screams and countless chugs of expensive Bud Light Lime.

The young crowd's energy never wavered throughout the day. You could say they were giddily undiscriminating in their cheers, so that during Gillis' set it was unclear who they were screaming for the most, Gillis, or Gillis sampling "Livin on a Prayer." Seven-dollar boardwalk fries? "Super awesome yeah!!" They paid $55 for a show, and a chilly afternoon and some rain was not going come between them and their fun.

By 9:30 p.m., as the Strokes were half finished, the two-lane road out of Merriweather was already backlogged with cars. But the party did not seem to be over.

With the Osama news all over Twitter, the social media-savvy crowd, who had been urged to tweet by festival organizers with the #sweetlife tag, responded with equal glee. "#sweetlife was awesome. Now, I'm going to party at the White House. No, really," one tweeted.

Said another, "#sweetlife was amazing and now Osama is dead. USA! USA!"

Photo: Crowd at Merriweather Post Pavilion during Sweetlife (Brian Kristra/B the Site); unidentified attendee playing beer pong; Sweetlife-branded cupcake, two for $5. (Writer's own)

Earlier: Interview with The Strokes' Nikolai Fraiture