Sitting in the center of the room, the last person you’d probably notice but the reason all these people were here, was Mike Watt, bassist, ringmaster and punk extraordinaire. Relaxing on a cruddy old sofa with food bits and loose change in the creases, Watt looked more like the janitor, or at least the roadie, than the main attraction. His dark hair and beard are speckled with gray, and his pliant face is lined; he wore a blue flannel shirt, old jeans and tan Converses. He sipped a beer and chuckled as Evan flung his arm in front of a bystander. “This is my accessory:” Evan crowed, showing off a pair of goggles worn as a bracelet. “He’s a free spirit,” Watt said affectionately.

Watt, 37, has been a musician for 15 years, but he’s only recently stepped toward the spotlight. The cavalcade-of-stars tour, bringing arena rock musicians into the kind of midsize clubs they haven’t played in years, supports Watt’s first solo album, “Ball-Hog or Tugboat?”, an ingeniously orchestrated effort teaming the bassist with 50 guest musicians, from Vedder, Dando and Grohl to members of Sonic Youth, Soul Asylum, Beastie Boys and others. (This tour ends May 20; Watt will take a different lineup out with him this summer to play Lollapalooza.) “Ball-Hog or Tugboat.’?” could have turned into a messy ego brigade, but instead it feels like a fabulously out-there ’60s jam session, with players coming and going through twisted takes on funk, punk and avant-garde jazz. “I had this weird idea that if I wrote the bass part right, maybe anybody could play guitar and drums and sing with me,” Watt says. “I know that’s kind of audacious. It’s the tail wagging the dog.”

Watt’s exquisite orneriness has earned him his high-caliber company. At a time when punk has become just another programming block on MTV and alternative rock is huge, chart-topping business, Watt is a hero-he’s everyone’s reminder of where the music came from. And where, given a choice, most of these guys would rather be. The afternoon of the Tramps show, Vedder was among the first to arrive and spent over an hour quietly setting up drum stands and microphones, just like everyone else. Watt learned punk in San Pedro, Calif., a rough harbor town near Los Angeles; he has a rusted bullet hole in his Econoline van that he picked up one night in Pedro. At 12, Watt adopted the bass at the suggestion of his best friend D. Boon’s mother, and by 1981 they had formed the Minutemen. Over the next five years they released some of the most brilliantly original albums of the ’80s punk wave-not your average three-chord skull-crushers, but tunefully and rhythmically complex songs that brought together buzzing guitars, fluid bass lines, free-jazz verse and left-wing politics. “I’m against rubber-stamp culture,” Watt says. “I like the freak flag to fly. You don’t know how many times me and D. Boon were pulled offstage. They did not believe we were in the band. I love that idea of the guys who weren’t supposed to be in the band, in the band.”

But D. Boon was killed in a ear crash in 1986. Watt formed fIREHOSE, which released five albums before breaking up last year. More than the band, it’s friends like Boon, Kurt Cobain and Darby Crash from the L.A. punk band the Germs that Watt misses the most. “See, we made a religion out off—ing music,” Watt says. “It’s not just a gig any-more. They didn’t call Watt up and ask him if that could happen. It just happened.”

That night, Watt went onstage in front of 800 people, with Vedder playing rhythm guitar and Grohl switching between guitar and drums. During the set, Watt turned to Grohl and grinned wildly. Dando jumped onstage with his vacuum cleaner and whirled it around until the twigs fell out. Vedder stood barely moving, staring intensely at his guitar as he played. And the freak flag flew high.