Upfront's Mark Suster created one of the most exclusive and glitziest gatherings in tech. But there's a dark side.

• Mark Suster is managing partner of Upfront Ventures, a Los Angeles venture firm
• Suster's fastidiousness has created what many now consider one of the best tech conferences of the year.
• But Suster's abrasive, take-no-prisoners approach has also alienated some startup founders and investors.

Inside an airy Los Angeles restaurant, the actor and Goop founder Gwyneth Paltrow and the billionaire developer Rick Caruso have just finished speaking on a VIP lunchtime panel. A few feet away, Serena Williams and her husband, the investor and Reddit founder Alexis Ohanian, are about to be served dessert.