Lady Gaga took her Hollywood golden age persona to a new level Thursday when she surprised a crowd at a Hollywood music venue to perform some jazzy standards.

Gaga appeared at the Black Rabbit Rose venue Thursday night where — get ready — Limp Bizkit frontman Fred Durst organizes a weekly live jazz night. (Who knew?!?)

Gaga floated onto the stage wearing a '50s-style halter dress, a large fur-looking stole, a beehive-esque bun, and some wicked cat eye. After greeting the band members with cheek kisses, she took the microphone and said "I'm here to ruin the party." The crowed whooped.

“My whole life, you know, I’ve been called irresponsible,” she told the crowd. “It doesn’t make me so mad because it’s kind of true… and I like to hear the truth.”

She then proceeded to sing the Frank Sinatra classic "Irresponsible" to a slower, more sultry time register than the more upbeat recording. As the saxophone soloist took a solo, she dipped down her jacket and waggled her shoulders. Watch the performance below.

Next, she moved on to Sinatra's classic "Fly Me to the Moon," inviting fans to sing along.

Lady Gaga apparently performs the Frank Sinatra jams at her Las Vegas residency. She's also a collaborator and BFF with jazzman Tony Bennett, who tweeted his support for Gaga after her performance of 'Shallow' at the Oscars, where she won her first Academy Award.

Tweet may have been deleted

Crashing a jazz show might be "irresponsible," but it's certainly all in good fun.