You simply never know what Britney Spears is going to do next.

In Vancouver last night, she pulled the plug on a sold-out Circus tour stop 15 minutes and three songs into her performance – inexplicably departing the stage and leaving a baffled audience in the dark for more than half an hour.

Boos ensued. Cigarette smoke was blamed.

"The building is awfully smoky," the announcer said during the unannounced hiatus. "It is uncomfortable for everyone on stage, including Ms. Spears."

People were told to extinguish cigarettes in the non-smoking building and the show would resume when the smoke cleared, the Vancouver Sun reports.

This left the fans "really pissed off," according to one concert-goer. "The break in the concert pretty much ruined it for everyone. The vibe was gone."

No word on whether she hit it with K-Fed during the break.

When she did return, the star delivered a Bollywood take on "Me Against the Music," followed by "Everytime" - during which she asked the crowd "What's up, Vancouver?" before again leaving the stage, some 90 seconds before the end of the song.

The concert concluded with Britney Spears singing her hit single, "Womanizer," and advising a still-restless crowd, "Vancouver, don't smoke weed."

What a lovable, sexy nut job.

After the show, Spears's publicist issued a statement saying "crew members above the stage became ill due to a ventilation issue." Poor Chase Benz!

Click to enlarge more pictures from this concert event ...

Britney Spears: Don't Smoke Weed!