Britney Spears Parties with Alli Sims, Tony Romo

As a guy who Carrie Underwood said bristled at the prospects of not being taken seriously as a football player while he was dating her, Tony Romo might want to think twice before hanging out with Britney Spears on his NFL bye week.

After a long, stressful custody hearing ("Eat it, lick it, snort it, f*%k it!") on Friday, Britney Spears hit the town with her longtime friend, Alli Sims - and naturally, Dallas Cowboys quarterback Romo, who's pals with Sims.

The pop star, dressed in a masquerade ball mask, and Alli Sims first made a quick stop at the L.A. restaurant Ketchup where Tony Romo was eating.

"[Britney] walked around the restaurant into the lounge where she met up with some people," an observer at Ketchup (possibly Heidi Montag) said.

"She didn't eat or drink ... [It] seemed like she was rounding up people to go to [out]. She was very friendly and smiley, in and out."

Another source says: "Alli Sims was meeting up with Tony Romo and his friends at Ketchup and Britney wanted to come along. Tony and Alli have been good friends. They've known each other for a little over a year. "

Later, Tony Romo met up with Alli Sims, Britney Spears and other pals at the hot night club Les Deux where they hung out for a friendly, low-key night upstairs.

Britney Spears was "sitting with her friends and Tony. Everyone was just hanging out. Britney was upbeat, really seemed fine."

Hey, as long as those little monsters Sean Preston and Jayden James aren't around, of course she's upbeat! Really, she seemed fine! Woo-hoo!

The following night, perhaps in a nod to Tony Romo, a source says that Alli Sims playfully dressed as a quarterback for Ryan Cabrera's costume party.

How lovely. We haven't heard much about Alli's signing career of late, sadly. In recent days, Romo has also been linked to One Tree Hill star Sophia Bush.