No way could this fan keep his “poker face.”

Lady Gaga just had to dance at the opening day of the Lollapalooza music bacchanal in Chicago, with the singer giving one hipster a handful of her famous fanny while she crowd-surfed in pasties and skivvies during the Semi-Precious Weapons gig. The pop icon, who was poo-pooed during her first appearance at the altfest in 2007, credited her fans with helping her to become “brave.”

“You have made me brave, you little monsters,” she told the crowd of 80,000 during her set on Friday, where she changed between a red cape and transparent dress. “Tonight, I want you to free yourself.”

PHOTOS: LADY GAGA’S AVANT-GARDE STYLE