John Mayer made a rare public appearance at the grand opening of Audemars Piguet’s Rodeo Drive boutique in Beverly Hills. Credit: Getty Images for Audemars Piguet

John Mayer palled around with James Corden during a rare public appearance at the grand opening of Audemars Piguet’s Rodeo Drive boutique in Beverly Hills.

Jonah Hill caught up with Aaron Paul at a celebration for Bryan Cranston at The Cinema Society's bash at Elyx House in NYC.

Ali Fedotowsky drove a taxi, surprising riders with a holiday trivia quiz and giving away a trip for two to Australia on behalf of Yellow Tail wine, in NYC.

Jamie-Lynn Sigler soothed son Beau after he took a small tumble at Disney’s Frozen on Ice premiere at the Staples Center in L.A.

Evan Ross gushed over daughter Jagger Snow at the Ui Culture App launch party at TCL Chinese Theatre in Hollywood.

Tyga and Pia Mia performed at the 2nd Annual Runway Wonderland Charity Event, sponsored by Tarte Cosmetics, at Hubble Studio in L.A.

Natalie Portman’s husband Benjamin Millepied got a standing ovation after dancing two solo pieces at the L.A. Dance Project 2015 Benefit in L.A.

—Neon Trees’ Tyler Glenn, Sam Hollander, Kevin Griffin, and the Band of Merrymakers spread some holiday cheer through Musicares’ Musicians On Call program by visiting Children’s Hospital in Westwood in L.A.

Loretta Lynn sang “Coal Miner’s Daughter” at a listening session for her new album, Full Circle, at Cutting Room in NYC.

Jill Zarin and her daughter Ally got their hair done at the Marie-Lou & D salon in NYC’s Soho neighborhood.

Boyz II Men performed to raise money for the Tiger Woods Foundation at the HERO World Challenge golf tournament in the Bahamas.

Taye Diggs, Lil’ Kim, and Raven-Symoné partied with the stars of Growing Up Hip Hop at the show’s premiere party in NYC.

Christina Applegate grabbed sushi with a girlfriend at Blue Ribbon in NYC.

Rosario Dawson attended the World Childhood Foundation USA's ThankYou Campaign and #EyesWideOpen initiative in NYC’s Harlem neighborhood.

Rachel Platten delivered gifts from Cracker Barrel and performed her hits "Fight Song" and "Stand By You" while visiting MacDill Air Force Base in Tampa, Fla.

Dita Von Teese celebrated the launch of her new lipstick for MAC Cosmetics, “Von Teese,” at MAC North Beverly in Beverly Hills.

Kaitlynn Carter and Foray Collective hosted a Marrakech-themed launch party for The Soukie Modern’s wedding bag collection at The Peninsula Beverly Hills.

Selling New York’s Tom Postilio and Mickey Conlon hosted a Frank Sinatra-themed party at the Edison Ballroom in NYC.

Rose McGowan celebrated the newly-renovated Living Room space at the W New York - Times Square with a screening of Ultimate Encore directed by Alan Cumming.

Audrina Patridge checked out the new Sweaty Betty store in L.A.’s Venice neighborhood.

Slash and Ryan Kwanten with Tilted Kilt hung out with fans at a special private screening of The Omen in L.A.

Dascha Polanco wore Cadar fine jewelry at the Joy premiere in NYC.

Steven Tyler and a group of friends enjoyed dinner hosted by Elizabeth Blau of CNBC’s Restaurant Startup at her restaurant Honey Salt in Las Vegas.

Cody Simpson, along with Coast House bandmates Corey Harper and Adrian Cota, performed at the Hollister Holiday Carnival to benefit Operation Warm at The Roxy Theatre in West Hollywood.

Andrea Bocelli sang at a private VIP concert for Pomellato and Baptist Health South Florida in Miami.

Lisa Vanderpump and Dame Joan Collins received UKares Foundation Awards at a benefit sponsored by Deep Eddy Vodka and Jose Cuervo at the British Consulate General’s residence in L.A.

Danica McKellar told reporters how much she loves watching former The Wonder Years co-star Fred Savage on his new show, Fox’s The Grinder, at Cirque du Soleil’s Kurios opening night at Dodger Stadium in L.A.

Will Ferrell wore a Samuelsohn Beckett Performance Suit on The Late Late Show hosted by Ryan Tubridy in Dublin, Ireland.

Jay Leno showered performer Jason Derulo with compliments at the Nobel Peace Prize concert in Oslo.

Shameless stars Emmy Rossum, Jeremy Allen White, Steve Howie, and Cameron Monaghan dined on steaks at DineAmic Group's steakhouse, Prime & Provisions, in Chicago.

Joe Jonas shopped with a group of kids from the Boys and Girls Club to kick off JCPenney's #GivingTuesday nationwide campaign in Brooklyn.