ATLANTIC CITY — If Avril Lavigne, Britney Spears and a dollar sign had a baby, it would be Ke$ha.

The 23-year-old singer, dubbed pop’s latest bad girl, headlined her first show — albeit briefly — Friday night before a sold-out Music Box at Borgata Hotel Casino and Spa.

Fans of Ke$ha got what they wanted. The singer, known for her distinctively pitchy sound mixed with a punky-girl rap and sometimes R-rated lyrics, brought her hits — currently, three of them on the radio and on various spots on the Billboard charts — and her funky, in-your-face style that has quickly earned her attention, both good and bad.

But the “Tik Tok” singer certainly knows how to watch the seconds on a clock. Ke$ha took to the stage at 9:45 p.m., and was finished with her radio hit by 10:15 p.m. She offered the crowd a quick “thank you” before running off.

The crowd, expecting an encore after her quick exit, began chanting her name. But after a few long minutes, the house lights came on.

“It’s over? I can’t believe I paid $40 for that,” one fan complained while leaving the theater.

Of course, Ke$ha only has one album, her current CD “Animal” — but the disc has 14 tracks, and she didn’t even sing all of those.

And, usually, a newer artist short on material will throw in a cover or two (whether fans want to hear them or not). Perhaps Ke$ha had somewhere else to be?

Ke$ha did show off her instrumental chops, playing keyboard, guitar, and even a cowbell (Christopher Walken would be proud) for her song “Dinosaur.”

She also flexed some vocal muscles — and yes, Ke$ha can sing. This is a shame, because her heavily synthesized pop vocals could really be sung by just about anyone. After “Tik Tok,” the talk-rapping gets old. Her single “Your Love is My Drug” is practically identical to “Tik Tok.”

The crowd was predominantly female and trended to the younger side — a few girls who appeared to be as young as 9 or 10 (accompanied by moms) were seen in more than a few seats. Those moms may have needed to do some explaining, as Ke$ha dropped a few f-bombs and talked about her “loser” ex-boyfriend “making out with a tranny,” among other stories.

Ke$ha’s band added some fun to the show, all wearing over-the-top, ’80s costumes and mugging for the crowd. Her male back-up dancers were dressed like two members of the Village People after a 3-day bender.

Opening for Ke$ha was rapper Dirt Nasty, who makes an appearance in the singer’s “Tik Tok” video but is perhaps best known for producing a song about a male body part that can’t be printed in a family newspaper.

Dirt, as he is often called, takes pride in his unapologetically raunchy rap lyrics, so it seemed like a bit of an odd mix to see the rapper performing before a crowd that included quite a few tweens.

Even Dirt Nasty himself realized his material wasn’t suited to the crowd, and censored most of his profanity.

“We’re going to tone it down a little bit tonight,” the rapper said as he scanned the predominantly 21-and-under crowd. “I see a lot of families here.”