Cool chick Chloë Sevigny has loads of equally hip friends to call on when she decides to throw a party. But even she was surprised by the turnout at the bash she hosted at Webster Hall Monday night — along with MAC Cosmetics, Self-Service Magazine and boutique Opening Ceremony — to celebrate her debut collection for the store and featuring a special performance by British punk rock band The Slits. By the time she arrived around 10:30 p.m., there was a line snaking around the block, three deep with grungesters, alternative chicks and general misfits.

"Oh my God, did you see how many people are out there?" exclaimed Sevigny to Slits lead singer Ari-Up as they made their way backstage. "It's, like, thousands!"

"They're all here for you," replied the red fishnet-bedecked belter. (She might have had a point, as many of the Opening Ceremony posters of Sevigny plastered all over the venue were quickly ripped off walls by eager fans.)

It has been 20 years since the band last performed at Webster Hall. "We really changed music, the culture and clothes. We were 30 years ahead of everyone. We were the first to wear tutus with Doc Martens, and then Madonna started dressing like us," claimed Ari-Up of the quartet, which formed in 1976.

Though you wouldn't guess it from Sevigny's Liberty print-laden collection, the actress-designer claims to be quite inspired by The Slits. But don't expect to see them making fashion week appearances a regular activity. "We're more individual," declared keyboardist Hollie.

They certainly attracted an eclectic crowd. Upstairs in the VIP area, Andy Samberg held hands with date Joanna Newsom, while Natasha Lyonne chilled with friends. Alexander Wang danced up a storm (apparently his own party Saturday night wasn't enough).

Meanwhile, Chris Benz hosted a comparatively civilized affair, inviting friends including Eva Amurri and Allison Sarofim, as well as his mom (who flew in from Seattle), for a genteel post-show dinner at Bette.

At the Gramercy Park Hotel, Julia Restoin Roitfeld, Theodora Richards and Lily Donaldson hosted a party for Joie's Serge Azria (Max's bro) at the Rose Bar until the wee hours. Donaldson, for her part, seemed game to burn the candle at both ends. "I can totally do it," the model said of her morning catwalk responsibilities. What's the trick, caffeine? "No, that's my Milan diet: espresso, espresso and more espresso."

A more adult crowd marked the return of Halston which, fittingly, revived classic nightspot Don Hill's. "I remember when I used to come here with André Balazs," said Helen Schifter. As for designer Marco Zanini, his date to the rock spot was his sister, Miki, who modeled a new Halston look. Tamara Mellon, however, chose a vintage Halston and arrived with beau Christian Slater. Meanwhile, Tamara's ex-husband Matthew Mellon's fiancé, Noelle Reno, was wearing another vintage Halston, a red chiffon style. "Tamara chose this for me," she said, before adding nervously, "I'm just trying to stay away from the red wine tonight."

SEVIGNY AND MISSONI PHOTOS BY SCOTT RUDD; BENZ PARTY BY KRISTEN SOMODY WHALEN; RICHARDS, HELLER, TRAINA BY NEIL RASMUS/PMC; LYONNE, MEYERS BY JAMIE MCCARTHY/WIREIMAGE; MELLONS BY MARC DIMOV/PMCv; SCOTT by FIRSTVIEW