Britney Spears was 'a pain' on set of How I Met Your Mother

Despite Britney Spears' appearance on 'How I Met Your Mother' getting the show its highest ever ratings, and being hailed a 'comeback' for the troubled star, her three-day stint on set of the CBS sitcom was a "pain", and caused delays in filming due to her "erratic demeanor", insiders claim.

"Her mood changes are so sudden, you don't understand where they're coming from," the insider tells Star magazine.

And at one point, the Toxic star got into a telephone fight with younger sister Jamie Lynn -- because the pregnant teen had called Britney's ex, Kevin Federline. Standing in a hallway, says a source, Britney was heard shouting into the phone, "You're turning on me like everyone else. First Mama wanted to sleep with Kevin and now you're calling him. And you live in a house I paid for!"

The 26-year-old then started asking people on the set if they liked puppies.

"It was a pain having her on the set," the insider says. "She made everything take so much longer because of all the drama she caused. Almost no one wants her back!"